Fix error diagnostics of c-macro-expand

* lisp/progmodes/cmacexp.el (c-macro-expansion): Don't bail out
too early if no start-marker string was found -- that generally
means cpp exited abnormally, and we still want to show its error
messages to the user.

1 files changed, 2 insertions, 2 deletions

diff --git a/lisp/progmodes/cmacexp.el b/lisp/progmodes/cmacexp.el
index 357625d10cf..19d0473c42d 100644
--- a/lisp/progmodes/cmacexp.el
+++ b/lisp/progmodes/cmacexp.el
@@ -364,8 +364,8 @@ Optional arg DISPLAY non-nil means show messages in the echo area."
             ;; Find and delete the mark of the start of the expansion.
             ;; Look for `# nn "file.c"' lines and delete them.
             (goto-char (point-min))
-            (search-forward startmarker)
-            (delete-region 1 (point)))
+            (if (search-forward startmarker nil t)
+                (delete-region 1 (point))))
           (while (re-search-forward (concat "^# [0-9]+ \""
                                             (regexp-quote filename)
                                             "\"") nil t)