Fix bug magickcore file loading freeze

This seemed to happen if the 'file' variable was NULL.  For some reason,
magickcore would just totally freeze.

libobs/graphics/graphics-magick.c

@@ -14,11 +14,17 @@ void gs_free_image_deps()
 
 texture_t gs_create_texture_from_file(const char *file)
 {
-	texture_t     tex        = NULL;
-	ImageInfo     *info      = CloneImageInfo(NULL);
-	ExceptionInfo *exception = AcquireExceptionInfo();
+	texture_t     tex = NULL;
+	ImageInfo     *info;
+	ExceptionInfo *exception;
 	Image         *image;
 
+	if (!file || !*file)
+		return NULL;
+
+	info      = CloneImageInfo(NULL);
+	exception = AcquireExceptionInfo();
+
 	strcpy(info->filename, file);
 	image = ReadImage(info, exception);
 	if (image) {