Mainly fix two mistakes that I made:

1. When the ERROR_END_OF_STREAM is returned from read, the input buffer is not initialized
   release it would lead to crash

2. The mPrevTimestampUs is not initialized and thus fail in the CHECK(mPrevTimestampUs, timeUs)

Change-Id: Id1e51575fb8b3ca48e80547efd3a3a82dfac773b

media/libstagefright/codecs/avc/enc/AVCEncoder.cpp

@@ -98,6 +98,7 @@ AVCEncoder::AVCEncoder(
     : mSource(source),
       mMeta(meta),
       mNumInputFrames(-1),
+      mPrevTimestampUs(-1),
       mStarted(false),
       mInputBuffer(NULL),
       mInputFrameData(NULL),

media/libstagefright/codecs/m4v_h263/enc/M4vH263Encoder.cpp

@@ -69,6 +69,7 @@ M4vH263Encoder::M4vH263Encoder(
       mMeta(meta),
       mNumInputFrames(-1),
       mNextModTimeUs(0),
+      mPrevTimestampUs(-1),
       mStarted(false),
       mInputBuffer(NULL),
       mInputFrameData(NULL),
@@ -292,8 +293,6 @@ status_t M4vH263Encoder::read(
     if (OK != mSource->read(&mInputBuffer, options)) {
         LOGE("Failed to read from data source");
         outputBuffer->release();
-        mInputBuffer->release();
-        mInputBuffer = NULL;
         return UNKNOWN_ERROR;
     }