GUI: prepare for macro height

src/gui/gui.cpp

@@ -3167,6 +3167,9 @@ FurnaceGUI::FurnaceGUI():
   noteOffOnReleaseKey(0),
   noteOffOnReleaseChan(0),
   arpMacroScroll(0),
+  volMacroHeight(0),
+  dutyMacroHeight(0),
+  waveMacroHeight(0),
   macroDragStart(0,0),
   macroDragAreaSize(0,0),
   macroDragTarget(NULL),

src/gui/gui.h

@@ -181,6 +181,8 @@ class FurnaceGUI {
 
   int arpMacroScroll;
 
+  int volMacroHeight, dutyMacroHeight, waveMacroHeight;
+
   ImVec2 macroDragStart;
   ImVec2 macroDragAreaSize;
   int* macroDragTarget;