Android: Allow specifying custom fonts in .xsys35rc

Now custom font files specified in .xsys35rc (as relative paths from the
ZIP root) can be loaded correctly.

This fixes #20 for Android.

src/font.c

@@ -80,7 +80,16 @@ void font_select(int type, int size) {
 		TTF_Font *fs;
 		
 		fs = TTF_OpenFontIndex(this.name[type], size, this.face[type]);
-		
+#ifdef __ANDROID__
+		// If `this.name[type]` is a custom font file specified in .xys35rc,
+		// SDL_RWFromFile used by TTF_OpenFontIndex does not work because it
+		// does not resolve relative path with the current directory. On the
+		// other hand, we can't just use fopen because SDL_RWFromFile can open
+		// apk assets and the default fonts are stored as assets.
+		FILE *fp = fopen(this.name[type], "r");
+		if (fp)
+			fs = TTF_OpenFontIndexRW(SDL_RWFromFP(fp, true), true, size, this.face[type]);
+#endif
 		if (fs == NULL) {
 			WARNING("%s is not found:\n", this.name[type]);
 			return;