Address a few other issues found by cppcheck

Thanks matthiaskrgr for running it.

src/config.cpp

@@ -1016,6 +1016,7 @@ struct config_has_value {
 	config_has_value(const std::string& name, const std::string& value)
 		: name_(name), value_()
 	{
+		// TODO: This is assigned here instead of in the init-list because attribute_value doesn't have a matching constructor
 		value_ = value;
 	}
 

src/game_board.cpp

@@ -44,6 +44,7 @@ game_board::game_board(const ter_data_cache & tdata, const config & level)
 game_board::game_board(const game_board & other)
 	: teams_(other.teams_)
 	, map_(new gamemap(*(other.map_)))
+	, labels_(other.labels_)
 	, unit_id_manager_(other.unit_id_manager_)
 	, units_(other.units_) {}
 

src/units/filter.hpp

@@ -55,6 +55,7 @@ public:
 	unit_filter(const unit_filter & o ) : impl_(o.impl_), max_matches_() {}
 	void swap(unit_filter & o) {
 		impl_.swap(o.impl_);
+		std::swap(max_matches_, o.max_matches_);
 	}
 	unit_filter & operator=(unit_filter o) {
 		swap(o);

src/utils/functional.hpp

@@ -36,7 +36,8 @@ namespace detail {
 	template<typename Ret, typename... T>
 	struct apply {
 		using result_type = void;
-		apply(std::function<Ret(T...)> fcn) : fcn(fcn) {}
+		apply(const std::function<Ret(T...)>& fcn) : fcn(fcn) {}
+		apply(Ret(*fcn)(T...)) : fcn(fcn) {}
 		void operator()(T... params) {
 			fcn(std::forward<T>(params)...);
 		}

src/xBRZ/xbrz.cpp

@@ -564,10 +564,10 @@ struct BlendResult
 struct Kernel_4x4 //kernel for preprocessing step
 {
     uint32_t
-    /**/a, b, c, d,
-    /**/e, f, g, h,
-    /**/i, j, k, l,
-    /**/m, n, o, p;
+    /**/a=0, b=0, c=0, d=0,
+    /**/e=0, f=0, g=0, h=0,
+    /**/i=0, j=0, k=0, l=0,
+    /**/m=0, n=0, o=0, p=0;
 
     Kernel_4x4() {}
 };
@@ -625,9 +625,9 @@ BlendResult preProcessCorners(const Kernel_4x4& ker, const xbrz::ScalerCfg& cfg)
 struct Kernel_3x3
 {
     uint32_t
-    /**/a,  b,  c,
-    /**/d,  e,  f,
-    /**/g,  h,  i;
+    /**/a=0,  b=0,  c=0,
+    /**/d=0,  e=0,  f=0,
+    /**/g=0,  h=0,  i=0;
 
     Kernel_3x3() {}
 };