android: fix crash on startup

src/imgui/imgui_impl_opengl3.cpp

@@ -125,9 +125,9 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_wid
     glDisable(GL_CULL_FACE);
     glDisable(GL_DEPTH_TEST);
     glEnable(GL_SCISSOR_TEST);
-#ifdef GL_POLYGON_MODE
-    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
-#endif
+    if (glPolygonMode) {
+        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+    }
 
     // Setup viewport, orthographic projection matrix
     // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right).
@@ -316,9 +316,9 @@ void ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data) {
         glEnable(GL_SCISSOR_TEST);
     else
         glDisable(GL_SCISSOR_TEST);
-#ifdef GL_POLYGON_MODE
-    glPolygonMode(GL_FRONT_AND_BACK, (GLenum)last_polygon_mode[0]);
-#endif
+    if (glPolygonMode) {
+        glPolygonMode(GL_FRONT_AND_BACK, (GLenum)last_polygon_mode[0]);
+    }
     glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
     glScissor(last_scissor_box[0], last_scissor_box[1], (GLsizei)last_scissor_box[2], (GLsizei)last_scissor_box[3]);
 }