propgui not showing all webcams

[danilogr]

I compiled the project using Visual Studio 2019 (v142) with SDL2 imported through vcpkg. All projects compiled and worked well except propgui.

progui uses RGBA for each camera texture, so it seems that some of my cameras were not filling in the A component (thereby causing their textures to become transparent).

The fix is rather simple in main.cpp - lines 48-51:

		for (i = 0; i < 256 * 256; i++)
			capture[device].mTargetBuf[i] = (capture[device].mTargetBuf[i] & 0xff00ff00) |
			((capture[device].mTargetBuf[i] & 0xff) << 16) |
			((capture[device].mTargetBuf[i] & 0xff0000) >> 16) | (0xff000000); // last bit adds alpha = 100%

I will submit a pull-request with my changes in case the @jarikomppa wants to merge it, but I am also leaving this note here in case others experience a similar problem ;).