Bug 1187076 - Warn at end of SPS buffers. r=jya

Previously we asserted if we tried to read past the end
of a buffer in parsing H.264 SPS headers. This only affected
debug builds, but the failures were reported as crashes in
automated testing.

Therefore, commute the assert to a warning and silently accept
bad data of this type. The read is safe with the first assert
removed because of the subsequent check, and a similar one in
the parent class.

media/libstagefright/binding/H264.cpp

@@ -26,7 +26,6 @@ class BitReader
 
   uint32_t ReadBits(size_t aNum)
   {
-    MOZ_ASSERT(mBitReader.numBitsLeft());
     MOZ_ASSERT(aNum <= 32);
     if (mBitReader.numBitsLeft() < aNum) {
       return 0;
@@ -48,7 +47,10 @@ class BitReader
       i++;
     }
     if (i == 32) {
-      MOZ_ASSERT(false);
+      // This can happen if the data is invalid, or if it's
+      // short, since ReadBit() will return 0 when it runs
+      // off the end of the buffer.
+      NS_WARNING("Invalid H.264 data");
       return 0;
     }
     uint32_t r = ReadBits(i);