Remove a redundant map access.

Change-Id: I37de97f08d37e4de0f413ef5248f9d55e2b168b3
Reviewed-on: https://code-review.googlesource.com/c/re2/+/59490
Reviewed-by: Matthew Fowles Kulukundis <kfm@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/regexp.cc b/re2/regexp.cc
index 2e1bfac..ca1318b 100644
--- a/re2/regexp.cc
+++ b/re2/regexp.cc
@@ -585,8 +585,7 @@
       // Record first occurrence of each name.
       // (The rule is that if you have the same name
       // multiple times, only the leftmost one counts.)
-      if (map_->find(*re->name()) == map_->end())
-        (*map_)[*re->name()] = re->cap();
+      map_->insert({*re->name(), re->cap()});
     }
     return ignored;
   }