Don't default-construct std::strings and then assign them.

Change-Id: I8c994d1e6a8d2ebe52eaa4f0132e0deb2ecfa5f3
diff --git a/src/dalvik_system_DexFile.cc b/src/dalvik_system_DexFile.cc
index cf4443b..f668cc9 100644
--- a/src/dalvik_system_DexFile.cc
+++ b/src/dalvik_system_DexFile.cc
@@ -163,7 +163,7 @@
   if (class_name.c_str() == NULL) {
     return NULL;
   }
-  const std::string descriptor = DotToDescriptor(class_name.c_str());
+  const std::string descriptor(DotToDescriptor(class_name.c_str()));
   const DexFile::ClassDef* dex_class_def = dex_file->FindClassDef(descriptor);
   if (dex_class_def == NULL) {
     return NULL;