Set the bytes per pixel for LUMINANCE_ALPHA to 2

This corrects a case where the camera was being used in a
multimedia example that was being streamed and the colors were
not correct as the some of the data was lost as a result.

Fixes: QTBUG-79181
Change-Id: I8ab02b525c6d54b0005f00d06969aa3ebbac4d20
Reviewed-by: VaL Doroshchuk <[email protected]>

Author: AndyShawQt

src/plugins/platforms/webgl/qwebglcontext.cpp

@@ -147,7 +147,7 @@ inline int imageSize(GLsizei width, GLsizei height, GLenum format, GLenum type,
         { GL_RGBA, GL_UNSIGNED_SHORT_5_5_5_1, 2 },
         { GL_RGB, GL_UNSIGNED_BYTE, 3 },
         { GL_RGB, GL_UNSIGNED_SHORT_5_6_5, 2 },
-        { GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, 1 },
+        { GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, 2 },
         { GL_LUMINANCE, GL_UNSIGNED_BYTE, 1 },
         { GL_ALPHA, GL_UNSIGNED_BYTE, 1 },