Regression: Accelerated GL ES waveforms are broken (on iOS)

[fwcd]

Bug Description

Accelerated waveforms currently do not work at all on iOS (same for non-stereo coloration):

The waveform stays black and the following message is spammed to the log:

warning [Main] QOpenGLShader::link: ERROR: OpenGL ES requires exactly one vertex and one fragment shader to validly link.

Non-accelerated waveforms work.

Version

7ecf6d0, which is based on the current 2.6/main

OS

iOS