DirectVolume: don't continue on invalid PARTN value

Change-Id: I1e434c5b47b40fabaf1e702d7f2e43a88c0497dc
diff --git a/DirectVolume.cpp b/DirectVolume.cpp
index 54da964..2ca0e72 100644
--- a/DirectVolume.cpp
+++ b/DirectVolume.cpp
@@ -187,8 +187,8 @@
     }
 
     if (part_num > MAX_PARTITIONS || part_num < 1) {
-        SLOGW("Invalid 'PARTN' value");
-        part_num = 1;
+        SLOGE("Invalid 'PARTN' value");
+        return;
     }
 
     if (part_num > mDiskNumParts) {