Codechange: silence some potentially uninitialized local variable errors

In these cases technically they are false positives, however dismissing the
alerts when the underlying code may make them true positives does not seem
like the safest solution.

src/company_gui.cpp

@@ -636,7 +636,7 @@ private:
 		const Company *c;
 		const Livery *livery, *default_livery = nullptr;
 		bool primary = widget == WID_SCL_PRI_COL_DROPDOWN;
-		byte default_col;
+		byte default_col = 0;
 
 		/* Disallow other company colours for the primary colour */
 		if (this->livery_class < LC_GROUP_RAIL && HasBit(this->sel, LS_DEFAULT) && primary) {