Skip (and warn for) blank lines in comments.dm

The THOR-Soar project was failing to load because the comments.dm has blank
lines, and those caused exceptions during loading (because `line.charAt(0)` was
always out of bounds). After removing the blank lines, the comments appeared
to be on the correct nodes, so we'll just ignore them. I do not know how the
blank lines showed up in the file, but I find it very worrisome.

src/main/java/edu/umich/soar/visualsoar/datamap/SoarWorkingMemoryReader.java

@@ -435,12 +435,20 @@ public static boolean readSafe(SoarWorkingMemoryModel swmm, Reader fr, Reader cr
             }
         }
 
-        //If the comment file exists, read in all its comments
+        // If the comment file exists, read in all its comments
         Vector<String> commentVec = new Vector<>();
         if (cr != null) {
             Scanner scanCR = new Scanner(cr);
+            int lineNum = 0;
             while (scanCR.hasNextLine()) {
-                commentVec.add(scanCR.nextLine());
+                lineNum++;
+                String line = scanCR.nextLine();
+                if (line.isEmpty()) {
+                    errors.add(
+                        new FeedbackListEntry("Warning:  ignoring blank line at comment.dm line " + lineNum));
+                    continue;
+                }
+                commentVec.add(line);
             }
         }