Update libpng 1.5 patch: check return values of png_get_PLTE() and
png_get_tRNS() before using the values to avoid using uninitialized values.

--- a/lib/cximage-6.0/CxImage/ximapng.cpp
+++ b/lib/cximage-6.0/CxImage/ximapng.cpp
@@ -178,12 +178,14 @@ bool CxImagePNG::Decode(CxFile *hFile)
 	int _num_palette;
 	png_colorp _palette;
 #if PNG_LIBPNG_VER > 10399
-	png_get_PLTE(png_ptr,info_ptr,&_palette,&_num_palette);
+	png_uint_32 _palette_ret;
+	_palette_ret = png_get_PLTE(png_ptr,info_ptr,&_palette,&_num_palette);
+	if (_palette_ret && _num_palette>0){
 #else
 	_num_palette=info_ptr->num_palette;
 	_palette=info_ptr->palette;
-#endif
 	if (_num_palette>0){
+#endif
 		SetPalette((rgb_color*)_palette,_num_palette);
 		SetClrImportant(_num_palette);
 	} else if (_bit_depth ==2) { //<DP> needed for 2 bpp grayscale PNGs
@@ -199,11 +201,13 @@ bool CxImagePNG::Decode(CxFile *hFile)
 	int _num_trans;
 	png_color_16p _trans_color;
 #if PNG_LIBPNG_VER > 10399
-	png_get_tRNS(png_ptr,info_ptr,&_trans_alpha,&_num_trans,&_trans_color);
+	png_uint_32 _trans_ret;
+	_trans_ret = png_get_tRNS(png_ptr,info_ptr,&_trans_alpha,&_num_trans,&_trans_color);
+	if (_trans_ret && _num_trans!=0){ //palette transparency
 #else
 	_num_trans=info_ptr->num_trans;
-#endif
 	if (_num_trans!=0){ //palette transparency
+#endif
 		if (_num_trans==1){
 			if (_color_type == PNG_COLOR_TYPE_PALETTE){
 #if PNG_LIBPNG_VER > 10399
@@ -219,7 +223,11 @@ bool CxImagePNG::Decode(CxFile *hFile)
 #endif
 			}
 		}
+#if PNG_LIBPNG_VER > 10399
+		if (_num_trans>1 && _trans_alpha!=NULL){
+#else
 		if (_num_trans>1){
+#endif
 			RGBQUAD* pal=GetPalette();
 			if (pal){
 				DWORD ip;