[Core/Sound] fixed Nuked YM2413 core ch8&ch9 modulator wave leakage into output (cf. https://github.com/nukeykt/Nuked-OPLL/issues/13)

core/sound/opll.c

@@ -39,6 +39,10 @@
  *          VRC VII decap and die shot.
  *
  *  version: 1.0
+ *
+ *  additional changes (EkeEke):
+ *  - fixed attack phase rates 11.1 to 11.3
+ *  - fixed ch8&ch9 modulator wave leakage into output (backported from nukeyt core version 1.0.2)
  */
 
 #include <string.h>
@@ -953,6 +957,9 @@ void OPLL_Operator(opll_t *chip) {
         }
     }
 
+    if (!(chip->rm_enable & 0x80))
+        routput = 0;
+
     chip->ch_out = ismod1 ? routput : (output>>3);
 }