Prepare to add hasSamplePtrHeader and hasSampleInstHeader in dispatch (WIP)

for refresh sample memory when loop/end pointer and instrument parameter changed. Also, this PR has minor code style fixes and add warning in MultiPCM sample map usage.

src/engine/platform/snes.cpp

@@ -964,6 +964,10 @@ size_t DivPlatformSNES::getSampleMemUsage(int index) {
   return index == 0 ? sampleMemLen : 0;
 }
 
+bool DivPlatformSNES::hasSamplePtrHeader(int index) {
+  return true;
+}
+
 bool DivPlatformSNES::isSampleLoaded(int index, int sample) {
   if (index!=0) return false;
   if (sample<0 || sample>32767) return false;