Powerup icons display incorrectly when bighud is on but resolution is low

[GooberRF]

This is super low priority because of how unlikely it is for anyone to ever run into the issue, but nevertheless...

To reproduce:

• Turn on bighud in launcher
• Set resolution to 640x480
• Launch game - the HUD automatically uses the original (non bighud) HUD elements because the resolution is so small
• Pick up an amp or invuln, the powerup icon still shows the large version even though bighud is being forced off due to resolution

Below are screenshots of what this bug looks like (top) and what it should look like with bighud disabled due to low screen resolution (bottom)