WebCodecs AV1 codec string validation is buggy

rdar://122084515
https://bugs.webkit.org/show_bug.cgi?id=268538

Reviewed by Eric Carlson.

We just validate the profile so just need to ensure it is there.
We fix the length check and add a '.' check.

Covered by AV1 test running on devices with AV1 decoders.

* Source/WebKit/GPUProcess/webrtc/LibWebRTCCodecsProxy.mm:
(WebKit::validateCodecString):

Canonical link: https://commits.webkit.org/274089@main

Source/WebKit/GPUProcess/webrtc/LibWebRTCCodecsProxy.mm

@@ -167,10 +167,11 @@ static bool validateCodecString(VideoCodecType codecType, const String& codecStr
         ASSERT(codecString.startsWith("vp09.0"_s));
         return true;
     case VideoCodecType::AV1:
-        if (codecString.startsWith("av01."_s) && codecString.length() > 7)
+        ASSERT(codecString.startsWith("av01."_s));
+        if (!codecString.startsWith("av01."_s) || codecString.length() < 7)
             return false;
         auto profile = codecString[5];
-        return profile == '0' || profile == '1' || profile == '2';
+        return (profile == '0' || profile == '1' || profile == '2') && codecString[6] == '.';
     }
     ASSERT_NOT_REACHED();
     return true;