Use -1 for map-value in r_forceAmbient

Allow using 0 as an actual value.

Author: VReaperV

src/engine/renderer/tr_bsp.cpp

@@ -4363,7 +4363,7 @@ void R_LoadEntities( lump_t *l, std::string &externalEntities )
 		// check for ambient color
 		else if ( !Q_stricmp( keyname, "_color" ) || !Q_stricmp( keyname, "ambientColor" ) )
 		{
-			if ( r_forceAmbient.Get() == 0 ) {
+			if ( r_forceAmbient.Get() == -1 ) {
 				sscanf( value, "%f %f %f", &tr.ambientLight[0], &tr.ambientLight[1],
 					&tr.ambientLight[2] );
 

src/engine/renderer/tr_init.cpp

@@ -226,8 +226,8 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 	cvar_t      *r_wolfFog;
 	cvar_t      *r_noFog;
 
-	Cvar::Range<Cvar::Cvar<float>> r_forceAmbient( "r_forceAmbient", "Minimal light amount in lightGrid", Cvar::NONE,
-		0.125f, 0.0f, 0.3f );
+	Cvar::Range<Cvar::Cvar<float>> r_forceAmbient( "r_forceAmbient", "Minimal light amount in lightGrid; -1 to use map value", Cvar::NONE,
+		0.125f, -1.0f, 0.3f );
 	Cvar::Cvar<float> r_ambientScale( "r_ambientScale", "Scale lightGrid produced by ambientColor keyword by this much", Cvar::CHEAT, 1.0 );
 	cvar_t      *r_lightScale;
 	cvar_t      *r_debugSort;