fix crash in lintChanges.py

scripts/maint/lintChanges.py

@@ -55,7 +55,10 @@ def lintfile(fname):
            '(' not in m.group(2)):
         warn("Missing subcategory on %s"%m.group(1))
 
-    isBug = ("bug" in m.group(1).lower() or "fix" in m.group(1).lower())
+    if m:
+        isBug = ("bug" in m.group(1).lower() or "fix" in m.group(1).lower())
+    else:
+        isBug = False
 
     contents = " ".join(contents.split())