WebGLRenderer: Fix transmission render target type check (#23885)

src/renderers/WebGLRenderer.js

@@ -1201,7 +1201,7 @@ function WebGLRenderer( parameters = {} ) {
 
 			_transmissionRenderTarget = new WebGLRenderTarget( 1, 1, {
 				generateMipmaps: true,
-				type: utils.convert( HalfFloatType ) !== null ? HalfFloatType : UnsignedByteType,
+				type: extensions.has( 'EXT_color_buffer_half_float' ) ? HalfFloatType : UnsignedByteType,
 				minFilter: LinearMipmapLinearFilter,
 				samples: ( isWebGL2 && _antialias === true ) ? 4 : 0
 			} );