Fix comparison sign warnings.

Bug:23213430

Change-Id: I6f2e2b03b968a569b122004b4803c5d17fccfb12
(cherry picked from commit 635bc8f90429b2fdcaf7f8d43f7f59bcd0fe951c)
diff --git a/media/libstagefright/MPEG4Extractor.cpp b/media/libstagefright/MPEG4Extractor.cpp
index f68c89f..c745198 100644
--- a/media/libstagefright/MPEG4Extractor.cpp
+++ b/media/libstagefright/MPEG4Extractor.cpp
@@ -1945,7 +1945,7 @@
                 ALOGV("chunk_data_size = %lld and data_offset = %lld",
                         chunk_data_size, data_offset);
 
-                if (chunk_data_size >= SIZE_MAX - 1) {
+                if (chunk_data_size < 0 || static_cast<uint64_t>(chunk_data_size) >= SIZE_MAX - 1) {
                     return ERROR_MALFORMED;
                 }
                 sp<ABuffer> buffer = new ABuffer(chunk_data_size + 1);