[0.4.x] libvisual: Fix conversion of color to uint32

[hartwork]

Original report: https://sourceforge.net/p/libvisual/bugs/18/

#include <stdint.h>
#include <stdio.h>

int main() {
        int r = 0x11;
        int g = 0x22;
        int b = 0x33;

        uint32_t colors;

        colors = (256 << 24) | (r << 16) | (g << 8) | b;
        printf("Old: 0x%08x\n", colors);

        colors = (255 << 24) | (r << 16) | (g << 8) | b;
        printf("New: 0x%08x\n", colors);

        return 0;
}

# gcc main.c && ./a.out
main.c: In function ‘main’:
main.c:11:23: warning: result of ‘256 << 24’ requires 34 bits to represent, but ‘int’ only has 32 bits [-Wshift-overflow=]
   11 |         colors = (256 << 24) | (r << 16) | (g << 8) | b;
      |                       ^~
Old: 0x00112233
New: 0xff112233

CC @dcb314

[grandchild]

You may consider writing 0xff instead of 255 to make it super obvious that the intent is to fill the MSB with all-ones.

[hartwork]

You may consider writing 0xff instead of 255 to make it super obvious that the intent is to fill the MSB with all-ones.

No objections, done. Thanks for the review!