lavf/img2: Add svg and svgz to allow reading image sequences.

Increase the return value for svg_probe() to make it != AVPROBE_SCORE_EXTENSION.

libavformat/img2.c

@@ -65,6 +65,8 @@ const IdStrMap ff_img_tags[] = {
     { AV_CODEC_ID_SUNRAST,    "im24"     },
     { AV_CODEC_ID_SUNRAST,    "im32"     },
     { AV_CODEC_ID_SUNRAST,    "sunras"   },
+    { AV_CODEC_ID_SVG,        "svg"      },
+    { AV_CODEC_ID_SVG,        "svgz"     },
     { AV_CODEC_ID_JPEG2000,   "j2c"      },
     { AV_CODEC_ID_JPEG2000,   "jp2"      },
     { AV_CODEC_ID_JPEG2000,   "jpc"      },

libavformat/img2dec.c

@@ -876,7 +876,7 @@ static int sunrast_probe(AVProbeData *p)
 static int svg_probe(AVProbeData *p)
 {
     if (av_match_ext(p->filename, "svg") || av_match_ext(p->filename, "svgz"))
-        return AVPROBE_SCORE_EXTENSION;
+        return AVPROBE_SCORE_EXTENSION + 1;
     return 0;
 }