avformat/img2dec: do not interpret the filename by default if a IO context has been opened

With this, user applications which use custom IO and have set a IO context will not have
their already opened IO context ignored and glob/seq being interpreted

Comments and tests from maintainers of user apps are welcome!
Liked-by: wm4 <nfxjfg@googlemail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/img2.h

@@ -34,7 +34,8 @@ enum PatternType {
     PT_GLOB_SEQUENCE,
     PT_GLOB,
     PT_SEQUENCE,
-    PT_NONE
+    PT_NONE,
+    PT_DEFAULT
 };
 
 typedef struct VideoDemuxData {

libavformat/img2dec.c

@@ -225,6 +225,13 @@ int ff_img_read_header(AVFormatContext *s1)
     }
 
     if (!s->is_pipe) {
+        if (s->pattern_type == PT_DEFAULT) {
+            if (s1->pb) {
+                s->pattern_type = PT_NONE;
+            } else
+                s->pattern_type = PT_GLOB_SEQUENCE;
+        }
+
         if (s->pattern_type == PT_GLOB_SEQUENCE) {
         s->use_glob = is_glob(s->path);
         if (s->use_glob) {
@@ -557,7 +564,7 @@ const AVOption ff_img_options[] = {
     { "framerate",    "set the video framerate",             OFFSET(framerate),    AV_OPT_TYPE_VIDEO_RATE, {.str = "25"}, 0, 0,   DEC },
     { "loop",         "force loop over input file sequence", OFFSET(loop),         AV_OPT_TYPE_BOOL,   {.i64 = 0   }, 0, 1,       DEC },
 
-    { "pattern_type", "set pattern type",                    OFFSET(pattern_type), AV_OPT_TYPE_INT,    {.i64=PT_GLOB_SEQUENCE}, 0,       INT_MAX, DEC, "pattern_type"},
+    { "pattern_type", "set pattern type",                    OFFSET(pattern_type), AV_OPT_TYPE_INT,    {.i64=PT_DEFAULT}, 0,       INT_MAX, DEC, "pattern_type"},
     { "glob_sequence","select glob/sequence pattern type",   0, AV_OPT_TYPE_CONST,  {.i64=PT_GLOB_SEQUENCE}, INT_MIN, INT_MAX, DEC, "pattern_type" },
     { "glob",         "select glob pattern type",            0, AV_OPT_TYPE_CONST,  {.i64=PT_GLOB         }, INT_MIN, INT_MAX, DEC, "pattern_type" },
     { "sequence",     "select sequence pattern type",        0, AV_OPT_TYPE_CONST,  {.i64=PT_SEQUENCE     }, INT_MIN, INT_MAX, DEC, "pattern_type" },