toke.c: S_is_existing_identifier: Handle lexicals

This code, looks for global variables, but it was not updated to also
handle lexical variables when they were added to the language.

This commit adds that handling

Author: khwilliamson

toke.c

@@ -4472,23 +4472,26 @@ S_is_existing_identifier(pTHX_ char *s, char *e, bool is_utf8)
 {
     /* This checks if the string from 's' to (e - 1) with utf8ness 'is_utf8' is
      * an identifier known to the program.  If so, it returns the length of
-     * the identifier.  If not, it returns 0
-     *
-     * khw: This only looks at global variables; lexicals came later, and this
-     * hasn't been updated.  Ouch!! */
+     * the identifier.  If not, it returns 0 */
 
     ptrdiff_t size = e - s;
 
     /* khw: scan_ident appears to need a 2-byte minimum; easiest to just add
-     * that than calculate a minimum. */
-    size += 2;
+     * that than calculate a minimum, Use 3 because we offset the output one
+     * byte to the right */
+    size += 3;
     char * tmpbuf;
     Newx(tmpbuf, size, char);
 
-    scan_ident(s, tmpbuf, size, FALSE);
+    /* scan_ident doesn't return the sigil, but pad_findmy_pv wants it */
+    scan_ident(s, tmpbuf + 1, size - 1, FALSE);
+    tmpbuf[0] = s[0];
+
+    Size_t len = strlen(tmpbuf) - 1;    /* Doesn't include sigil */
 
-    Size_t len = strlen(tmpbuf);
-    if (! gv_fetchpvn_flags(tmpbuf, len,
+    PADOFFSET slot = pad_findmy_pv(tmpbuf, 0);
+    if (   slot == NOT_IN_PAD
+        && ! gv_fetchpvn_flags(tmpbuf + 1, len,
                                (is_utf8) ? SVf_UTF8 : 0,
                                (s[0] == '@')
                                 ? SVt_PVAV