swscale/utils: fill xyz tables only when they will be used

makes the first call to sws_getContext() 1ms faster
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/utils.c

@@ -985,8 +985,6 @@ int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4],
     c->srcRange   = srcRange;
     c->dstRange   = dstRange;
 
-    fill_xyztables(c);
-
     if ((isYUV(c->dstFormat) || isGray(c->dstFormat)) && (isYUV(c->srcFormat) || isGray(c->srcFormat)))
         return -1;
 
@@ -1077,6 +1075,8 @@ static void handle_formats(SwsContext *c)
     c->dst0Alpha |= handle_0alpha(&c->dstFormat);
     c->srcXYZ    |= handle_xyz(&c->srcFormat);
     c->dstXYZ    |= handle_xyz(&c->dstFormat);
+    if (c->srcXYZ || c->dstXYZ)
+        fill_xyztables(c);
 }
 
 SwsContext *sws_alloc_context(void)