Drop now superfluous checks for zero width/height

These have been introduced as fix for bug 72337[1], while the same
issue had a simpler fix for upstream[2], because the helper functions
already were internal.

[1] <https://bugs.php.net/72337>
[2] <libgd/libgd@77309c4>

Author: cmb69

ext/gd/libgd/gd_interpolation.c

@@ -1069,10 +1069,6 @@ gdImageScaleTwoPass(const gdImagePtr src, const unsigned int src_width, const un
 	gdImagePtr dst;
 	int scale_pass_res;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	/* Convert to truecolor if it isn't; this code requires it. */
 	if (!src->trueColor) {
 		gdImagePaletteToTrueColor(src);
@@ -1127,10 +1123,6 @@ gdImageScaleNearestNeighbour(gdImagePtr im, const unsigned int width, const unsi
 	unsigned long  dst_offset_y = 0;
 	unsigned int i;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	dst_img = gdImageCreateTrueColor(new_width, new_height);
 
 	if (dst_img == NULL) {
@@ -1184,10 +1176,6 @@ static gdImagePtr gdImageScaleBilinearPalette(gdImagePtr im, const unsigned int
 	gdImagePtr new_img;
 	const int transparent = im->transparent;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	new_img = gdImageCreateTrueColor(new_width, new_height);
 	if (new_img == NULL) {
 		return NULL;
@@ -1285,10 +1273,6 @@ static gdImagePtr gdImageScaleBilinearTC(gdImagePtr im, const unsigned int new_w
 	long i;
 	gdImagePtr new_img;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	new_img = gdImageCreateTrueColor(new_width, new_height);
 	if (!new_img){
 		return NULL;
@@ -1389,10 +1373,6 @@ gdImageScaleBicubicFixed(gdImagePtr src, const unsigned int width, const unsigne
 	unsigned int dst_offset_y = 0;
 	long i;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	/* impact perf a bit, but not that much. Implementation for palette
 	   images can be done at a later point.
 	*/
@@ -1672,10 +1652,6 @@ gdImageRotateNearestNeighbour(gdImagePtr src, const float degrees, const int bgC
     new_width = bbox.width;
     new_height = bbox.height;
 
-	if (new_width == 0 || new_height == 0) {
-		return NULL;
-	}
-
 	dst = gdImageCreateTrueColor(new_width, new_height);
 	if (!dst) {
 		return NULL;