Fix runaway comment bug (finally!)

examples/easy/rabbitwithgun/sensors

@@ -1,2 +0,0 @@
-50 0 0 1
-70 0 50 0

forf.c

@@ -586,8 +586,13 @@ forf_parse_stream(struct forf_env *env,
 
     /* Handle comments */
     if (comment) {
-      if (')' == c) {
+      switch (c) {
+        case EOF:
+          env->error = forf_error_parse;
+          return pos;
+        case ')':
           comment = 0;
+          break;
       }
       continue;
     }