ART: Do not use std::<container>::at().

These functions are specified as throwing std::out_of_range
and we do not use exceptions.

Test: m
Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I67c365ed6d779c101a18b9f386c751c48ca76e16
diff --git a/patchoat/patchoat.cc b/patchoat/patchoat.cc
index 0beca1f..97b315e 100644
--- a/patchoat/patchoat.cc
+++ b/patchoat/patchoat.cc
@@ -539,7 +539,7 @@
 
     space_to_memmap_map.emplace(space, std::move(image));
     PatchOat p = PatchOat(isa,
-                          space_to_memmap_map.at(space).get(),
+                          space_to_memmap_map[space].get(),
                           space->GetLiveBitmap(),
                           space->GetMemMap(),
                           delta,