Merge branch 'master' into jgrpp

# Conflicts:
#	.github/workflows/release.yml
#	bin/CMakeLists.txt
#	src/dock_gui.cpp
#	src/lang/brazilian_portuguese.txt
#	src/lang/catalan.txt
#	src/lang/czech.txt
#	src/lang/dutch.txt
#	src/lang/english.txt
#	src/lang/english_US.txt
#	src/lang/estonian.txt
#	src/lang/finnish.txt
#	src/lang/french.txt
#	src/lang/german.txt
#	src/lang/hungarian.txt
#	src/lang/indonesian.txt
#	src/lang/italian.txt
#	src/lang/japanese.txt
#	src/lang/korean.txt
#	src/lang/lithuanian.txt
#	src/lang/luxembourgish.txt
#	src/lang/norwegian_bokmal.txt
#	src/lang/polish.txt
#	src/lang/portuguese.txt
#	src/lang/romanian.txt
#	src/lang/russian.txt
#	src/lang/serbian.txt
#	src/lang/simplified_chinese.txt
#	src/lang/slovak.txt
#	src/lang/spanish.txt
#	src/lang/spanish_MX.txt
#	src/lang/swedish.txt
#	src/lang/tamil.txt
#	src/lang/ukrainian.txt
#	src/lang/vietnamese.txt
#	src/newgrf.cpp
#	src/newgrf_gui.cpp
#	src/object_gui.cpp
#	src/pathfinder/yapf/yapf_costrail.hpp
#	src/pathfinder/yapf/yapf_node_rail.hpp
#	src/rail_cmd.cpp
#	src/roadveh_cmd.cpp
#	src/town_cmd.cpp
#	src/vehicle.cpp
#	src/water_cmd.cpp

src/blitter/factory.hpp

@@ -61,13 +61,14 @@ protected:
 			name(name), description(description)
 	{
 		if (usable) {
+			Blitters &blitters = GetBlitters();
+			assert(blitters.find(this->name) == blitters.end());
 			/*
 			 * Only add when the blitter is usable. Do not bail out or
 			 * do more special things since the blitters are always
 			 * instantiated upon start anyhow and freed upon shutdown.
 			 */
-			std::pair<Blitters::iterator, bool> P = GetBlitters().insert(Blitters::value_type(this->name, this));
-			assert(P.second);
+			blitters.insert(Blitters::value_type(this->name, this));
 		} else {
 			DEBUG(driver, 1, "Not registering blitter %s as it is not usable", name);
 		}