Use separate CharSetFilter types for signed and unsigned decimal

src/settings_gui.cpp

@@ -2811,8 +2811,11 @@ struct GameSettingsWindow : Window {
 
 				this->valuewindow_entry = pe;
 				if (sd->flags & SF_DECIMAL1 || (sd->flags & SF_GUI_VELOCITY && _settings_game.locale.units_velocity == 3)) {
+					CharSetFilter charset_filter = CS_NUMERAL_DECIMAL; //default, only numeric input and decimal point allowed
+					if (sd->min < 0) charset_filter = CS_NUMERAL_DECIMAL_SIGNED; // special case, also allow '-' sign for negative input
+
 					SetDParam(0, value64);
-					ShowQueryString(STR_JUST_DECIMAL1, STR_CONFIG_SETTING_QUERY_CAPTION, 10, this, CS_NUMERAL_DECIMAL, QSF_ENABLE_DEFAULT);
+					ShowQueryString(STR_JUST_DECIMAL1, STR_CONFIG_SETTING_QUERY_CAPTION, 10, this, charset_filter, QSF_ENABLE_DEFAULT);
 				} else {
 					CharSetFilter charset_filter = CS_NUMERAL; //default, only numeric input allowed
 					if (sd->min < 0) charset_filter = CS_NUMERAL_SIGNED; // special case, also allow '-' sign for negative input

src/string.cpp

@@ -602,9 +602,11 @@ bool IsValidChar(WChar key, CharSetFilter afilter)
 		case CS_NUMERAL:       return (key >= '0' && key <= '9');
 		case CS_NUMERAL_SIGNED:  return (key >= '0' && key <= '9') || key == '-';
 #if !defined(STRGEN) && !defined(SETTINGSGEN)
-		case CS_NUMERAL_DECIMAL: return (key >= '0' && key <= '9') || key == '.' || key == '-' || key == GetDecimalSeparatorChar();
+		case CS_NUMERAL_DECIMAL: return (key >= '0' && key <= '9') || key == '.' || key == GetDecimalSeparatorChar();
+		case CS_NUMERAL_DECIMAL_SIGNED: return (key >= '0' && key <= '9') || key == '.' || key == '-' || key == GetDecimalSeparatorChar();
 #else
-		case CS_NUMERAL_DECIMAL: return (key >= '0' && key <= '9') || key == '.' || key == '-';
+		case CS_NUMERAL_DECIMAL: return (key >= '0' && key <= '9') || key == '.';
+		case CS_NUMERAL_DECIMAL_SIGNED: return (key >= '0' && key <= '9') || key == '.' || key == '-';
 #endif
 		case CS_NUMERAL_SPACE: return (key >= '0' && key <= '9') || key == ' ';
 		case CS_ALPHA:         return IsPrintable(key) && !(key >= '0' && key <= '9');

src/string_type.h

@@ -27,7 +27,8 @@ enum CharSetFilter {
 	CS_ALPHANUMERAL,      ///< Both numeric and alphabetic and spaces and stuff
 	CS_NUMERAL,           ///< Only numeric ones
 	CS_NUMERAL_SIGNED,    ///< Only numeric ones, and minus/negative
-	CS_NUMERAL_DECIMAL,   ///< Only numeric, decimal separaters, and minus/negative
+	CS_NUMERAL_DECIMAL,   ///< Only numeric, decimal separaters
+	CS_NUMERAL_DECIMAL_SIGNED, ///< Only numeric, decimal separaters, and minus/negative
 	CS_NUMERAL_SPACE,     ///< Only numbers and spaces
 	CS_ALPHA,             ///< Only alphabetic values
 	CS_HEXADECIMAL,       ///< Only hexadecimal characters