Remove the checking before accessing to function pointers

Bug: angleproject:5490
Bug: chromium:1161513
Change-Id: I96c5c463a9fd5a337d09f6cefe7836ff52bea90f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2601071
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>

scripts/code_generation_hashes/OpenGL_dispatch_table.json

@@ -4,11 +4,11 @@
   "src/libANGLE/renderer/angle_format.py":
     "32ba71942c0fd00e6807104f1bb80a3c",
   "src/libANGLE/renderer/gl/DispatchTableGL_autogen.cpp":
-    "02e276847f77b21a1c5d3c4885001ca5",
+    "aa8b6e65dfb22da4cc82207ef4668d4f",
   "src/libANGLE/renderer/gl/DispatchTableGL_autogen.h":
     "bb30a343213143900e8d72dd4b00bcb0",
   "src/libANGLE/renderer/gl/generate_gl_dispatch_table.py":
-    "2aaada12f9932fcd113cd4e9728e676a",
+    "69b2c89e66a92373e600af8be16e5576",
   "src/libANGLE/renderer/gl/gl_bindings_data.json":
     "6f46f537e07b457850c060ef0c7b76c5",
   "src/libANGLE/renderer/gl/null_functions.cpp":

src/libANGLE/renderer/gl/generate_gl_dispatch_table.py

@@ -112,8 +112,7 @@ dispatch_table_source_template = """// GENERATED FILE - DO NOT EDIT.
 #include "libANGLE/renderer/gl/null_functions.h"
 #endif  // defined(ANGLE_ENABLE_OPENGL_NULL)
 
-// Check for nullptr so extensions do not overwrite core imports.
-#define ASSIGN(NAME, FP) if (!FP) FP = reinterpret_cast<decltype(FP)>(loadProcAddress(NAME))
+#define ASSIGN(NAME, FP) do {{ FP = reinterpret_cast<decltype(FP)>(loadProcAddress(NAME)); }} while (0)
 
 namespace rx
 {{
@@ -122,17 +121,17 @@ DispatchTableGL::DispatchTableGL() = default;
 void DispatchTableGL::initProcsDesktopGL(const gl::Version &version, const std::set<std::string> &extensions)
 {{
 #if defined(ANGLE_ENABLE_OPENGL_DESKTOP)
-{gl_data}
-
 {gl_extensions_data}
+
+{gl_data}
 #endif  // defined(ANGLE_ENABLE_OPENGL_DESKTOP)
 }}
 
 void DispatchTableGL::initProcsGLES(const gl::Version &version, const std::set<std::string> &extensions)
 {{
-{gles2_data}
-
 {gles2_extensions_data}
+
+{gles2_data}
 }}
 
 void DispatchTableGL::initProcsSharedExtensions(const std::set<std::string> &extensions)
@@ -144,17 +143,17 @@ void DispatchTableGL::initProcsSharedExtensions(const std::set<std::string> &ext
 void DispatchTableGL::initProcsDesktopGLNULL(const gl::Version &version, const std::set<std::string> &extensions)
 {{
 #if defined(ANGLE_ENABLE_OPENGL_DESKTOP)
-{gl_null_data}
-
 {gl_null_extensions_data}
+
+{gl_null_data}
 #endif  // defined(ANGLE_ENABLE_OPENGL_DESKTOP)
 }}
 
 void DispatchTableGL::initProcsGLESNULL(const gl::Version &version, const std::set<std::string> &extensions)
 {{
-{gles2_null_data}
-
 {gles2_null_extensions_data}
+
+{gles2_null_data}
 }}
 
 void DispatchTableGL::initProcsSharedExtensionsNULL(const std::set<std::string> &extensions)