add getWantPreNote()

currently only C64 system requires this

src/engine/platform/abstract.cpp

@@ -90,6 +90,10 @@ bool DivDispatch::getDCOffRequired() {
   return false;
 }
 
+bool DivDispatch::getWantPreNote() {
+  return false;
+}
+
 const char* DivDispatch::getEffectName(unsigned char effect) {
   return NULL;
 }

src/engine/platform/c64.cpp

@@ -513,6 +513,10 @@ bool DivPlatformC64::getDCOffRequired() {
   return true;
 }
 
+bool DivPlatformC64::getWantPreNote() {
+  return true;
+}
+
 void DivPlatformC64::reset() {
   for (int i=0; i<3; i++) {
     chan[i]=DivPlatformC64::Channel();

src/engine/platform/c64.h

@@ -97,6 +97,7 @@ class DivPlatformC64: public DivDispatch {
     void setFlags(unsigned int flags);
     void notifyInsChange(int ins);
     bool getDCOffRequired();
+    bool getWantPreNote();
     DivMacroInt* getChanMacroInt(int ch);
     void notifyInsDeletion(void* ins);
     void poke(unsigned int addr, unsigned short val);