Another library_webgl.js cleanup. NFC (#21458)

Similar to #21457 but this one actually as a code size saving

src/library_webgl.js

@@ -1641,16 +1641,18 @@ for (/**@suppress{duplicate}*/var i = 0; i < {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
       // those always when possible.
       if (GLctx.currentPixelUnpackBufferBinding) {
         GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, pixels);
-      } else if (pixels) {
+        return;
+      }
+      if (pixels) {
         var heap = heapObjectForWebGLType(type);
-        GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, heap, toTypedArrayIndex(pixels, heap));
-      } else {
-        GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, null);
+        var index = toTypedArrayIndex(pixels, heap);
+        GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, heap, index);
+        return;
       }
-      return;
     }
 #endif
-    GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, pixels ? emscriptenWebGLGetTexPixelData(type, format, width, height, pixels, internalFormat) : null);
+    var pixelData = pixels ? emscriptenWebGLGetTexPixelData(type, format, width, height, pixels, internalFormat) : null;
+    GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, pixelData);
   },
 
   glTexSubImage2D__deps: ['$emscriptenWebGLGetTexPixelData'

test/code_size/hello_webgl2_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 569,
   "a.html.gz": 379,
-  "a.js": 4589,
-  "a.js.gz": 2341,
+  "a.js": 4539,
+  "a.js.gz": 2315,
   "a.wasm": 10451,
   "a.wasm.gz": 6724,
-  "total": 15609,
-  "total_gz": 9444
+  "total": 15559,
+  "total_gz": 9418
 }

test/code_size/hello_webgl2_wasm2js.json

@@ -1,8 +1,8 @@
 {
   "a.html": 354,
   "a.html.gz": 266,
-  "a.js": 22323,
-  "a.js.gz": 11632,
-  "total": 22677,
-  "total_gz": 11898
+  "a.js": 22273,
+  "a.js.gz": 11608,
+  "total": 22627,
+  "total_gz": 11874
 }

test/code_size/hello_webgl_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 569,
   "a.html.gz": 379,
-  "a.js": 4075,
-  "a.js.gz": 2170,
+  "a.js": 4056,
+  "a.js.gz": 2152,
   "a.wasm": 10451,
   "a.wasm.gz": 6724,
-  "total": 15095,
-  "total_gz": 9273
+  "total": 15076,
+  "total_gz": 9255
 }

test/code_size/hello_webgl_wasm2js.json

@@ -1,8 +1,8 @@
 {
   "a.html": 354,
   "a.html.gz": 266,
-  "a.js": 21794,
-  "a.js.gz": 11450,
-  "total": 22148,
-  "total_gz": 11716
+  "a.js": 21775,
+  "a.js.gz": 11436,
+  "total": 22129,
+  "total_gz": 11702
 }