Fix oatdump for no image

Added MemMap::Init if we dont initialize the runtime.

Bug: 18000219
Change-Id: I1bd715e18838919c0773db5fa25623348326baa6
diff --git a/oatdump/oatdump.cc b/oatdump/oatdump.cc
index 1f2c0aa..2649ab7 100644
--- a/oatdump/oatdump.cc
+++ b/oatdump/oatdump.cc
@@ -2225,6 +2225,8 @@
     runtime.reset(StartRuntime(args.boot_image_location_,
                                args.image_location_,
                                args.instruction_set_));
+  } else {
+    MemMap::Init();
   }
 
   if (args.oat_filename_ != nullptr) {