CameraMetadata: Fix String tag update null character issue

String8.size() doesn't count the null character in whatever case. But camera
metadata tag android.jpeg.gpsProcessingMethod need a null-terminited string.

Bug: 13679912
Change-Id: I91e742702b16b9ab9b42f9822de189a9a96e8e53
diff --git a/camera/CameraMetadata.cpp b/camera/CameraMetadata.cpp
index 6b726e0..1567cd1 100644
--- a/camera/CameraMetadata.cpp
+++ b/camera/CameraMetadata.cpp
@@ -273,7 +273,8 @@
     if ( (res = checkType(tag, TYPE_BYTE)) != OK) {
         return res;
     }
-    return updateImpl(tag, (const void*)string.string(), string.size());
+    // string.size() doesn't count the null termination character.
+    return updateImpl(tag, (const void*)string.string(), string.size() + 1);
 }
 
 status_t CameraMetadata::updateImpl(uint32_t tag, const void *data,