Call glGetError() after glFinish(), not glFlush().

As I understand it, both glGetError() and glFinish() are serializing
and blockig, so it makes more sense to call them at the same time.
glFlush() does not block.

src/render/rendergl1.cpp

@@ -809,6 +809,10 @@ void OpenGl1Renderer::FlushFrame() {
     UnSelectPrimitive();
 
     glFlush();
+}
+
+void OpenGl1Renderer::FinishFrame() {
+    glFinish();
 
     GLenum error = glGetError();
     if(error != GL_NO_ERROR) {
@@ -816,10 +820,6 @@ void OpenGl1Renderer::FlushFrame() {
     }
 }
 
-void OpenGl1Renderer::FinishFrame() {
-    glFinish();
-}
-
 std::shared_ptr<Pixmap> OpenGl1Renderer::ReadFrame() {
     int width  = camera.width  * camera.pixelRatio;
     int height = camera.height * camera.pixelRatio;

src/render/rendergl3.cpp

@@ -669,6 +669,10 @@ void OpenGl3Renderer::FlushFrame() {
     points.Clear();
 
     glFlush();
+}
+
+void OpenGl3Renderer::FinishFrame() {
+    glFinish();
 
     GLenum error = glGetError();
     if(error != GL_NO_ERROR) {
@@ -676,10 +680,6 @@ void OpenGl3Renderer::FlushFrame() {
     }
 }
 
-void OpenGl3Renderer::FinishFrame() {
-    glFinish();
-}
-
 void OpenGl3Renderer::Clear() {
     ViewportCanvas::Clear();
     pixmapCache.CleanupUnused();