Incorrect variable assignment in examples using imgprovider.cpp

## Issue description

Incorrectly assigned variable indicated in the notification. 
When using fallback in the chooseStreamResolution function, it causes the entire application to crash.

https://github.com/AxisCommunications/acap3-examples/blob/cd47c6fd12a56269fb731ece77091dbacc3bfdbe/using-opencv/app/imgprovider.cpp#L272C4-L272C30

## System setup

- acap3-examples

