Fix bug in error detection code, where a zero-length string was causing a traceback

Fixes #5064

lib/ansible/utils/__init__.py

@@ -403,7 +403,7 @@ Or:
                 match = True
             elif middle.startswith('"') and not middle.endswith('"'):
                 match = True
-            if middle[0] in [ '"', "'" ] and middle[-1] in [ '"', "'" ] and probline.count("'") > 2 or probline.count("'") > 2:
+            if len(middle) > 0 and middle[0] in [ '"', "'" ] and middle[-1] in [ '"', "'" ] and probline.count("'") > 2 or probline.count("'") > 2:
                 unbalanced = True
             if match:
                 msg = msg + """