RENDERER: Fix opengl1/OpenGL2 crash in levelshot command

Setting packAlign was removed [1] and later set to 0 [2] and this caused
PADP( ..., 0 ) to return NULL which later gets passed to R_GammaCorrect()
and crashed.

It seems I left packAlign in my PNG/levelshot changes [3] even though
it's not needed in R_LevelShot().

Set packAlign to 1 which is single byte alignment and doesn't allocate
additional memory. PADP( ..., 1 ) returns the same address and it
doesn't crash later.

1: b514a01
2: 688f4f5
3: ioquake/ioq3#262

code/renderergl1/tr_init.c

@@ -488,7 +488,7 @@ static void R_LevelShot(screenshotType_e type, const char *ext) {
 	size_t offset = 0, memcount;
 	int spadlen, rpadlen;
 	int padwidth, linelen;
-	GLint packAlign = 0;
+	GLint packAlign = 1;
 	byte *src, *dst;
 	int x, y;
 	int r, g, b;

code/renderergl2/tr_init.c

@@ -577,7 +577,7 @@ static void R_LevelShot(screenshotType_e type, const char *ext) {
 	size_t offset = 0, memcount;
 	int spadlen, rpadlen;
 	int padwidth, linelen;
-	GLint packAlign = 0;
+	GLint packAlign = 1;
 	byte *src, *dst;
 	int x, y;
 	int r, g, b;