Fix LocalUpdatableMaps

Avoid accessing nullptr of already deleted entry.

Add new unit tests that pass with the fix and fail without.

Test: fixes unwinding in ART gcstress tests
Test: All unit tests pass.
Change-Id: Ideb00e2adc899904dd6aeb5dad3fb6fad150322d
diff --git a/libunwindstack/Maps.cpp b/libunwindstack/Maps.cpp
index 5da73e4..250e600 100644
--- a/libunwindstack/Maps.cpp
+++ b/libunwindstack/Maps.cpp
@@ -149,9 +149,10 @@
       }
 
       // Never delete these maps, they may be in use. The assumption is
-      // that there will only every be a handfull of these so waiting
+      // that there will only every be a handful of these so waiting
       // to destroy them is not too expensive.
       saved_maps_.emplace_back(std::move(info));
+      search_map_idx = old_map_idx + 1;
       maps_[old_map_idx] = nullptr;
       total_entries--;
     }