Fix static analyzer warnings

It was unhappy about uninitialized values potentially being passed into
calls. The warnings were:

frameworks/av/media/libstagefright/DataSource.cpp:254:22: warning:
Function call argument is an uninitialized value

frameworks/av/media/libstagefright/MPEG4Extractor.cpp:4528:17: warning:
Function call argument is an uninitialized value

(The latter was complaining about both `size` and `offset`)

Bug: None
Test: Still builds; static analyzer is now less unhappy.
Change-Id: If8befe493267a5de20e46787b50d854c49d208a3
diff --git a/media/libstagefright/DataSource.cpp b/media/libstagefright/DataSource.cpp
index 163a527..2cfadba 100644
--- a/media/libstagefright/DataSource.cpp
+++ b/media/libstagefright/DataSource.cpp
@@ -231,7 +231,7 @@
         }
 
         String8 cacheConfig;
-        bool disconnectAtHighwatermark;
+        bool disconnectAtHighwatermark = false;
         KeyedVector<String8, String8> nonCacheSpecificHeaders;
         if (headers != NULL) {
             nonCacheSpecificHeaders = *headers;
diff --git a/media/libstagefright/MPEG4Extractor.cpp b/media/libstagefright/MPEG4Extractor.cpp
index 9392e7d..02be033 100644
--- a/media/libstagefright/MPEG4Extractor.cpp
+++ b/media/libstagefright/MPEG4Extractor.cpp
@@ -4412,8 +4412,8 @@
         // fall through
     }
 
-    off64_t offset;
-    size_t size;
+    off64_t offset = 0;
+    size_t size = 0;
     uint32_t cts, stts;
     bool isSyncSample;
     bool newBuffer = false;