Backends: OpenGL3: Fix to avoid calling glBindSampler() with version <= 3.2 (#3467, #1985)

(nb: GLEW sets the define we previously used)

examples/imgui_impl_opengl3.cpp

@@ -263,10 +263,12 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_wid
     glUseProgram(g_ShaderHandle);
     glUniform1i(g_AttribLocationTex, 0);
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-#ifdef GL_SAMPLER_BINDING
-    glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
+    
+#if (!defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3))
+    if(g_GlVersion > 320)
+        glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
 #endif
-
+    
     (void)vertex_array_object;
 #ifndef IMGUI_IMPL_OPENGL_ES2
     glBindVertexArray(vertex_array_object);
@@ -299,8 +301,10 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     glActiveTexture(GL_TEXTURE0);
     GLuint last_program; glGetIntegerv(GL_CURRENT_PROGRAM, (GLint*)&last_program);
     GLuint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, (GLint*)&last_texture);
-#ifdef GL_SAMPLER_BINDING
-    GLuint last_sampler; glGetIntegerv(GL_SAMPLER_BINDING, (GLint*)&last_sampler);
+#if (!defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3))
+    GLuint last_sampler; 
+    if(g_GlVersion > 320)
+        glGetIntegerv(GL_SAMPLER_BINDING, (GLint*)&last_sampler);
 #endif
     GLuint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, (GLint*)&last_array_buffer);
 #ifndef IMGUI_IMPL_OPENGL_ES2
@@ -391,8 +395,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     // Restore modified GL state
     glUseProgram(last_program);
     glBindTexture(GL_TEXTURE_2D, last_texture);
-#ifdef GL_SAMPLER_BINDING
-    glBindSampler(0, last_sampler);
+#if (!defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3))
+    if(g_GlVersion > 320)
+        glBindSampler(0, last_sampler);
 #endif
     glActiveTexture(last_active_texture);
 #ifndef IMGUI_IMPL_OPENGL_ES2