Fix some warnings in nanovg code

dgl/src/nanovg/fontstash.h

@@ -854,6 +854,7 @@ int fonsAddFont(FONScontext* stash, const char* name, const char* path)
 	FILE* fp = 0;
 	int dataSize = 0;
 	unsigned char* data = NULL;
+	size_t ignore;
 
 	// Read in the font data.
 	fp = fopen(path, "rb");
@@ -863,7 +864,7 @@ int fonsAddFont(FONScontext* stash, const char* name, const char* path)
 	fseek(fp,0,SEEK_SET);
 	data = (unsigned char*)malloc(dataSize);
 	if (data == NULL) goto error;
-	fread(data, 1, dataSize, fp);
+	ignore = fread(data, 1, dataSize, fp);
 	fclose(fp);
 	fp = 0;
 
@@ -873,6 +874,8 @@ error:
 	if (data) free(data);
 	if (fp) fclose(fp);
 	return FONS_INVALID;
+
+	FONS_NOTUSED(ignore);
 }
 
 int fonsAddFontMem(FONScontext* stash, const char* name, unsigned char* data, int dataSize, int freeData)

dgl/src/nanovg/stb_image.h

@@ -4127,7 +4127,8 @@ static stbi_uc *stbi__gif_load_next(stbi__context *s, stbi__gif *g, int *comp, i
 static stbi_uc *stbi__gif_load(stbi__context *s, int *x, int *y, int *comp, int req_comp)
 {
    stbi_uc *u = 0;
-   stbi__gif g={0};
+   stbi__gif g;
+   memset(&g, 0, sizeof(stbi__gif));
 
    u = stbi__gif_load_next(s, &g, comp, req_comp);
    if (u == (void *) 1) u = 0;  // end of animated gif marker