img: Add ability to check whether optional image collection happened

A bit later we'd need to check whether cinfo collector
opened an image or not due to file absense.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/protobuf.h

@@ -49,6 +49,7 @@ struct collect_image_info {
 
 #define COLLECT_SHARED		0x1	/* use shared memory for obj-s */
 #define COLLECT_OPTIONAL	0x2	/* image file may be missing */
+#define COLLECT_HAPPENED	0x4	/* image was opened and collected */
 
 extern int collect_image(struct collect_image_info *);
 

protobuf.c

@@ -648,6 +648,7 @@ int collect_image(struct collect_image_info *cinfo)
 			return -1;
 	}
 
+	cinfo->flags |= COLLECT_HAPPENED;
 	if (cinfo->flags & COLLECT_SHARED) {
 		o_alloc = shmalloc;
 		o_free = shfree_last;