Examples: imgui_impl_opengl3.cpp Using #ifdef GL_SAMPLER_BINDING instead of if (glBindSampler) (#1985)

diff --git a/examples/imgui_impl_opengl3.cpp b/examples/imgui_impl_opengl3.cpp
index db2ba6a..90d0008 100644
--- a/examples/imgui_impl_opengl3.cpp
+++ b/examples/imgui_impl_opengl3.cpp
@@ -163,8 +163,9 @@
     glUseProgram(g_ShaderHandle);
     glUniform1i(g_AttribLocationTex, 0);
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-    if (glBindSampler) glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
-
+#ifdef GL_SAMPLER_BINDING
+    glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
+#endif
     // Recreate the VAO every time 
     // (This is to easily allow multiple GL contexts. VAO are not shared among GL contexts, and we don't track creation/deletion of windows so we don't have an obvious key to use to cache them.)
     GLuint vao_handle = 0;
@@ -220,7 +221,9 @@
     // Restore modified GL state
     glUseProgram(last_program);
     glBindTexture(GL_TEXTURE_2D, last_texture);
-    if (glBindSampler) glBindSampler(0, last_sampler);
+#ifdef GL_SAMPLER_BINDING
+    glBindSampler(0, last_sampler);
+#endif
     glActiveTexture(last_active_texture);
     glBindVertexArray(last_vertex_array);
     glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);