win: fix dump textures and box art saves when path contains non-ascii

Texture dumping and local boxart scraper were failing on windows if
image path contains non-ascii chars. nonwide::fopen must be used.

core/rend/CustomTexture.cpp

@@ -280,7 +280,19 @@ void CustomTexture::DumpTexture(u32 hash, int w, int h, TextureType textype, voi
 	}
 
 	stbi_flip_vertically_on_write(1);
-	stbi_write_png(path.str().c_str(), w, h, STBI_rgb_alpha, dst_buffer, 0);
+	const auto& savefunc = [](void *context, void *data, int size) {
+		FILE *f = nowide::fopen((const char *)context, "wb");
+		if (f == nullptr)
+		{
+			WARN_LOG(RENDERER, "Dump texture: can't save to file %s: error %d", context, errno);
+		}
+		else
+		{
+			fwrite(data, 1, size, f);
+			fclose(f);
+		}
+	};
+	stbi_write_png_to_func(savefunc, (void *)path.str().c_str(), w, h, STBI_rgb_alpha, dst_buffer, 0);
 
 	free(dst_buffer);
 }

core/rend/boxart/scraper.cpp

@@ -144,7 +144,19 @@ void OfflineScraper::scrape(GameBoxart& item)
 					{
 						stbi_flip_vertically_on_write(0);
 						item.setBoxartPath(makeUniqueFilename("gdtex.png"));
-						stbi_write_png(item.boxartPath.c_str(), w, h, 4, out.data(), 0);
+						const auto& savefunc = [](void *context, void *data, int size) {
+							FILE *f = nowide::fopen((const char *)context, "wb");
+							if (f == nullptr)
+							{
+								WARN_LOG(COMMON, "can't create local file %s: error %d", context, errno);
+							}
+							else
+							{
+								fwrite(data, 1, size, f);
+								fclose(f);
+							}
+						};
+						stbi_write_png_to_func(savefunc, (void *)item.boxartPath.c_str(), w, h, 4, out.data(), 0);
 					}
 				}
 			}