prepare to add function to find sub-songs

for import

src/engine/fileOps/it.cpp

@@ -623,6 +623,9 @@ bool DivEngine::loadIT(unsigned char* file, size_t len) {
     }
     ds.systemLen=(maxChan+32)>>5;
 
+    // find subsongs
+    ds.findSubSongs();    
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();

src/engine/fileOps/mod.cpp

@@ -417,6 +417,9 @@ bool DivEngine::loadMod(unsigned char* file, size_t len) {
       ds.ins.push_back(ins);
     }
     ds.insLen=ds.ins.size();
+
+    // find subsongs
+    ds.findSubSongs();
     
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;

src/engine/fileOps/s3m.cpp

@@ -999,6 +999,9 @@ bool DivEngine::loadS3M(unsigned char* file, size_t len) {
       }
     }
 
+    // find subsongs
+    ds.findSubSongs();    
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();

src/engine/fileOps/xm.cpp

@@ -370,6 +370,9 @@ bool DivEngine::loadXM(unsigned char* file, size_t len) {
 
     ds.sampleLen=ds.sample.size();
 
+    // find subsongs
+    ds.findSubSongs();
+
     if (active) quitDispatch();
     BUSY_BEGIN_SOFT;
     saveLock.lock();