Merge #13241: scripted-diff: Avoid temporary copies when looping over std::map

9b72c988a0 scripted-diff: Avoid temporary copies when looping over std::map (Ben Woosley)

Pull request description:

  The ::value_type of the std::map/std::multimap/std::unordered_map containers is
  std::pair<const Key, T>. Dropping the const results in an unnecessary copy,
  for example in C++11 range-based loops.

  For this I started with a more general scripted diff, then narrowed it down
  based on the inspection showing that all actual map/multimap/unordered_map
  variables used in loops start with m or have map in the name.

Tree-SHA512: b656d66b69ffa1eb954124aa8ae2bc5436ca50262abefa93bdda55cfcdaffc5ff90cd40539051a2bd06355ba69ddf245265cc8764eebff66d761b3aec06155a9

src/init.cpp

@@ -632,7 +632,7 @@ static void CleanupBlockRevFiles()
     // keeping a separate counter.  Once we hit a gap (or if 0 doesn't exist)
     // start removing block files.
     int nContigCounter = 0;
-    for (const std::pair<std::string, fs::path>& item : mapBlockFiles) {
+    for (const std::pair<const std::string, fs::path>& item : mapBlockFiles) {
         if (atoi(item.first) == nContigCounter) {
             nContigCounter++;
             continue;