[gtk+] build: Don't try to detect vulkan library if the header wasn't found.

[Benjamin Otte <otte src gnome org>]

commit 3e9811d91cf0c4e1101b1eed913c950819ad55fd
Author: Benjamin Otte <otte redhat com>
Date:   Fri Dec 9 21:17:27 2016 +0100

    build: Don't try to detect vulkan library if the header wasn't found.
    
    We've already failed. No need to fail again.

 configure.ac |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index b0d3767..5988696 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1323,8 +1323,9 @@ fi
 
 if test "x$enable_vulkan" != "xno"; then
       vulkan_error=""
-      AC_CHECK_HEADER([vulkan/vulkan.h], [], [vulkan_error="Vulkan header not found"])
-      AC_CHECK_LIB([vulkan], [vkCreateInstance], [], [vulkan_error="Vulkan library not found"])
+      AC_CHECK_HEADER([vulkan/vulkan.h],
+          [AC_CHECK_LIB([vulkan], [vkCreateInstance], [], [vulkan_error="Vulkan library not found"])],
+          [vulkan_error="Vulkan header not found"])
       if test "x$vulkan_error" != "x"; then
           if "x$enable_vulkan" = "xyes"; then
               AC_MSG_ERROR($vulkan_error)