Fix clip when scrolling ImSequencer out of view

Related to #57: clip rectangle not correct when slots out of parent
window.

This is a reimplementation of #57 which no longer merges cleanly.

ImSequencer.cpp

@@ -267,7 +267,7 @@ namespace ImSequencer
                   */
                   // clip content
 
-         draw_list->PushClipRect(childFramePos, childFramePos + childFrameSize);
+         draw_list->PushClipRect(childFramePos, childFramePos + childFrameSize, true);
 
          // draw item names in the legend rect on the left
          size_t customHeight = 0;
@@ -291,9 +291,6 @@ namespace ImSequencer
             customHeight += sequence->GetCustomHeight(i);
          }
 
-         // clipping rect so items bars are not visible in the legend on the left when scrolled
-         //
-
          // slots background
          customHeight = 0;
          for (int i = 0; i < sequenceCount; i++)
@@ -312,7 +309,7 @@ namespace ImSequencer
             customHeight += localCustomHeight;
          }
 
-         draw_list->PushClipRect(childFramePos + ImVec2(float(legendWidth), 0.f), childFramePos + childFrameSize);
+         draw_list->PushClipRect(childFramePos + ImVec2(float(legendWidth), 0.f), childFramePos + childFrameSize, true);
 
          // vertical frame lines in content area
          for (int i = sequence->GetFrameMin(); i <= sequence->GetFrameMax(); i += frameStep)