rtsp: remove CHECK to ignore unsupported tracks

RFC 3551 specifies a number of static A/V profiles for media
payload. These don't use the 'rtpmap' or 'fmtp' properties in the
session description, and thus need to be handled differently.
For now, we just ignore these types as they are very rarely used.

The previous paragraph was taken from
https://android-review.googlesource.com/#/c/240630/,
author David Williams <david.williams@sonymobile.com>.

Bug: 29493841
Change-Id: I12581447f18344ac503fe427e3c940a85d44644e
diff --git a/media/libstagefright/rtsp/ASessionDescription.cpp b/media/libstagefright/rtsp/ASessionDescription.cpp
index 47573c3..8b0331a 100644
--- a/media/libstagefright/rtsp/ASessionDescription.cpp
+++ b/media/libstagefright/rtsp/ASessionDescription.cpp
@@ -214,11 +214,13 @@
 
     char key[32];
     snprintf(key, sizeof(key), "a=rtpmap:%lu", x);
-
-    CHECK(findAttribute(index, key, desc));
-
-    snprintf(key, sizeof(key), "a=fmtp:%lu", x);
-    if (!findAttribute(index, key, params)) {
+    if (findAttribute(index, key, desc)) {
+        snprintf(key, sizeof(key), "a=fmtp:%lu", x);
+        if (!findAttribute(index, key, params)) {
+            params->clear();
+        }
+    } else {
+        desc->clear();
         params->clear();
     }
 }