Fix taking screenshots whose width is not congruent to 0 mod 4.

Closes #3537.

lib/ivis_opengl/screen.cpp

@@ -432,6 +432,7 @@ void screenDoDumpToDiskIfRequired(void)
 			return;
 		}
 	}
+	glPixelStorei(GL_PACK_ALIGNMENT, 1);
 	glReadPixels(0, 0, image.width, image.height, GL_RGB, GL_UNSIGNED_BYTE, image.bmp);
 
 	iV_saveImage_PNG(fileName, &image);