avformat/img2: Change enum to int, which is accessed via AVOption as int

This fixes depending on implementation defined behavior
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/img2.h

@@ -30,6 +30,12 @@
 #include <glob.h>
 #endif
 
+enum PatternType {
+    PT_GLOB_SEQUENCE,
+    PT_GLOB,
+    PT_SEQUENCE
+};
+
 typedef struct VideoDemuxData {
     const AVClass *class;  /**< Class for private options. */
     int img_first;
@@ -44,7 +50,7 @@ typedef struct VideoDemuxData {
     int width, height;      /**< Set by a private option. */
     AVRational framerate;   /**< Set by a private option. */
     int loop;
-    enum { PT_GLOB_SEQUENCE, PT_GLOB, PT_SEQUENCE } pattern_type;
+    int pattern_type; /**< PatternType */
     int use_glob;
 #if HAVE_GLOB
     glob_t globstate;