Fix reading RTSystems CSV files

A number of things weren't right with this, likely for a while, since
we had no tests or examples in the tree. This adds three user-supplied
sample files and a test to hopefully keep it working. Fixes:

- Ignore blank entries
- Tolerate a missing "Channel Number" column
- Support the "Scan" (meaning not skip) column type
- Fix detection by being looser about what we look for

Fixes #11389

chirp/drivers/generic_csv.py

@@ -231,6 +231,10 @@ def _load(self, f):
 
             try:
                 mem = self._parse_csv_data_line(header, line)
+                if mem is None:
+                    LOG.debug('Line %i did not contain a valid memory',
+                              lineno)
+                    continue
                 if mem.number is None:
                     raise Exception("Invalid Location field" % lineno)
             except Exception as e:
@@ -450,6 +454,7 @@ class RTCSVRadio(CSVRadio):
         "On":     "S",
         "P Scan": "P",
         "Skip":   "S",
+        "Scan":   "",
         }
 
     TMODE_MAP = {
@@ -462,13 +467,17 @@ class RTCSVRadio(CSVRadio):
         "On":   True,
     }
 
+    MODE_MAP = {
+        'FM Narrow': 'NFM',
+    }
+
     ATTR_MAP = {
         "Channel Number":    (int,   "number"),
         "Receive Frequency": (chirp_common.parse_freq, "freq"),
         "Offset Frequency":  (chirp_common.parse_freq, "offset"),
         "Offset Direction":  (lambda v:
                               RTCSVRadio.DUPLEX_MAP.get(v, v), "duplex"),
-        "Operating Mode":    (str,   "mode"),
+        "Operating Mode":    (lambda v: RTCSVRadio.MODE_MAP.get(v, v), 'mode'),
         "Name":              (str,   "name"),
         "Tone Mode":         (lambda v:
                               RTCSVRadio.TMODE_MAP.get(v, v), "tmode"),
@@ -484,6 +493,10 @@ class RTCSVRadio(CSVRadio):
         "Comment":           (str,   "comment"),
         }
 
+    def __init__(self, pipe):
+        self._last_loaded = 0
+        super().__init__(pipe)
+
     def _clean_duplex(self, headers, line, mem):
         if mem.duplex == "split":
             try:
@@ -511,6 +524,21 @@ def _clean_ctone(self, headers, line, mem):
         mem.ctone = mem.rtone
         return mem
 
+    def _clean_number(self, headers, line, mem):
+        if 'Channel Number' not in headers and self.memories:
+            # Some RTSystems software generates this with an empty header name?
+            self._last_loaded += 1
+            mem.number = self._last_loaded
+            LOG.debug('No location column, calculated %i from %r',
+                      mem.number, self.memories[-1])
+        return mem
+
+    def _parse_csv_data_line(self, headers, line):
+        val = get_datum_by_header(headers, line, "Receive Frequency")
+        if not val.strip():
+            return
+        return super()._parse_csv_data_line(headers, line)
+
     @classmethod
     def match_model(cls, filedata, filename):
         """Match files ending in .csv and using RT Systems column names."""
@@ -522,8 +550,13 @@ def match_model(cls, filedata, filename):
         except UnicodeDecodeError:
             # CSV files are text
             return False
+
+        try:
+            firstline, rest = filedata.split('\n', 1)
+            firstline_fields = firstline.split(',')
+        except Exception as e:
+            LOG.warning('Failed to detect file as RTCSV: %s', e)
+            return False
+
         return filename.lower().endswith("." + cls.FILE_EXTENSION) and \
-            filedata.startswith("Channel Number,Receive Frequency,"
-                                "Transmit Frequency,Offset Frequency,"
-                                "Offset Direction,Operating Mode,"
-                                "Name,Tone Mode,CTCSS,DCS")
+            'Receive Frequency' in firstline_fields