add bounds checking for mPartMinors[]

Change-Id: I6d5b26756c8434d6396f3535252608ce61eabfd8
diff --git a/DirectVolume.cpp b/DirectVolume.cpp
index ce5b892..0ac1a0c 100644
--- a/DirectVolume.cpp
+++ b/DirectVolume.cpp
@@ -186,6 +186,11 @@
         part_num = 1;
     }
 
+    if (part_num > MAX_PARTITIONS || part_num < 1) {
+        SLOGW("Invalid 'PARTN' value");
+        part_num = 1;
+    }
+
     if (part_num > mDiskNumParts) {
         mDiskNumParts = part_num;
     }