Fix DexFile_isDexOptNeeded to clear an error_msg in a recoverable case

Change-Id: Id4a6d0ab8fb259fa0edcc18ce768b33e95afc28a
diff --git a/runtime/native/dalvik_system_DexFile.cc b/runtime/native/dalvik_system_DexFile.cc
index af09a1c..55a56d6 100644
--- a/runtime/native/dalvik_system_DexFile.cc
+++ b/runtime/native/dalvik_system_DexFile.cc
@@ -242,9 +242,16 @@
                                               &error_msg)) {
         if (kVerboseLogging) {
           LOG(INFO) << "DexFile_isDexOptNeeded precompiled file " << odex_filename
-              << " is up-to-date checksum compared to " << filename.c_str();
+              << " has an up-to-date checksum compared to " << filename.c_str();
         }
         return JNI_FALSE;
+      } else {
+        if (kVerboseLogging) {
+          LOG(INFO) << "DexFile_isDexOptNeeded found precompiled file " << odex_filename
+              << " with an out-of-date checksum compared to " << filename.c_str()
+              << ": " << error_msg;
+        }
+        error_msg.clear();
       }
     }
   }