fix combobox issue, pad scissor by 1px

src/node_canvas.cpp

@@ -63,6 +63,14 @@ void NodeCanvas::clear_context()
 
 void NodeCanvas::draw()
 {
+    // sanity checks
+    float zoom = root()->m_zoom;
+    if (zoom == 0.f)
+        zoom = 1.f;
+    auto box = m_clip * zoom;
+    if (box.z == 0 || box.w == 0)
+        return;
+
     GLint vp[4];
     GLfloat cc[4];
     glGetIntegerv(GL_VIEWPORT, vp);
@@ -73,8 +81,6 @@ void NodeCanvas::draw()
 
     glDisable(GL_SCISSOR_TEST);
 
-    float zoom = root()->m_zoom;
-    auto box = m_clip * zoom;
     glm::ivec4 c = (glm::ivec4)glm::vec4(box.x, (int)(vp[3] - box.y - box.w), box.z, box.w);
 
     //m_canvas->m_cam_rot = m_pan * 0.003f;