Handle error result from DrmManagerClient correctly

readAtDRM() must handle the case when DrmManagerClient::pread()
returns an error (-1) correctly. This is a degrade in Android L.

Change-Id: Id7ff124d178e26931dddac5ac73697cfe6da501c
diff --git a/include/media/stagefright/FileSource.h b/include/media/stagefright/FileSource.h
index a981d1c..266168b 100644
--- a/include/media/stagefright/FileSource.h
+++ b/include/media/stagefright/FileSource.h
@@ -56,7 +56,7 @@
     sp<DecryptHandle> mDecryptHandle;
     DrmManagerClient *mDrmManagerClient;
     int64_t mDrmBufOffset;
-    size_t mDrmBufSize;
+    ssize_t mDrmBufSize;
     unsigned char *mDrmBuf;
 
     ssize_t readAtDRM(off64_t offset, void *data, size_t size);
diff --git a/media/libstagefright/FileSource.cpp b/media/libstagefright/FileSource.cpp
index 565f156..37053ec 100644
--- a/media/libstagefright/FileSource.cpp
+++ b/media/libstagefright/FileSource.cpp
@@ -166,7 +166,7 @@
     }
 
     if (mDrmBuf != NULL && mDrmBufSize > 0 && (offset + mOffset) >= mDrmBufOffset
-            && (offset + mOffset + size) <= (mDrmBufOffset + mDrmBufSize)) {
+            && (offset + mOffset + size) <= static_cast<size_t>(mDrmBufOffset + mDrmBufSize)) {
         /* Use buffered data */
         memcpy(data, (void*)(mDrmBuf+(offset+mOffset-mDrmBufOffset)), size);
         return size;
@@ -177,7 +177,7 @@
                 DRM_CACHE_SIZE, offset + mOffset);
         if (mDrmBufSize > 0) {
             int64_t dataRead = 0;
-            dataRead = size > mDrmBufSize ? mDrmBufSize : size;
+            dataRead = size > static_cast<size_t>(mDrmBufSize) ? mDrmBufSize : size;
             memcpy(data, (void*)mDrmBuf, dataRead);
             return dataRead;
         } else {