read: Move logic for getting a previous character into a read function

This ties related logic together, making it less of a hack and easier
to maintain, as well as accessible by all parsers if needed.

tagmanager/ctags/get.c

@@ -801,10 +801,7 @@ process:
 					 * 	"xxx(raw)xxx";
 					 *
 					 * which is perfectly valid (yet probably very unlikely). */
-					const unsigned char *base = (unsigned char *) vStringValue (File.line);
-					int prev = '\n';
-					if (File.currentLine - File.ungetchIdx - 2 >= base)
-						prev = (int) *(File.currentLine - File.ungetchIdx - 2);
+					int prev = fileGetNthPrevC (1, 0);
 
 					if (! isident (prev))
 					{

tagmanager/ctags/read.c

@@ -501,6 +501,18 @@ extern int fileGetc (void)
     return c;
 }
 
+/* returns the nth previous character (0 meaning current), or def if nth cannot
+ * be accessed.  Note that this can't access previous line data. */
+extern int fileGetNthPrevC (unsigned int nth, int def)
+{
+	const unsigned char *base = (unsigned char *) vStringValue (File.line);
+
+	if (File.currentLine - File.ungetchIdx - 1 - nth >= base)
+		return (int) *(File.currentLine - File.ungetchIdx - 1 - nth);
+	else
+		return def;
+}
+
 extern int fileSkipToCharacter (int c)
 {
 	int d;

tagmanager/ctags/read.h

@@ -102,6 +102,7 @@ extern boolean fileOpen (const char *const fileName, const langType language);
 extern boolean fileEOF (void);
 extern void fileClose (void);
 extern int fileGetc (void);
+extern int fileGetNthPrevC (unsigned int nth, int def);
 extern int fileSkipToCharacter (int c);
 extern void fileUngetc (int c);
 extern const unsigned char *fileReadLine (void);