docchecker: remove naked except clause

This is fixing for 'naked except clause' check-code rule.

check-code has overlooked this, because a file isn't recognized as one
to be checked (this problem is fixed by subsequent patch).

doc/docchecker

@@ -48,7 +48,7 b' def main():'
     try:
       with open(f) as file:
         work(file)
-    except:
-      print("failed to process %s" % f)
+    except BaseException as e:
+      print("failed to process %s: %s" % (f, e))
 
 main()