tweak: add missing return statement
 [rsc] --rw-rw-r-- M 1328934 glenda sys 38997 Mar 28 11:06 sys/src/cmd/tweak.c
	/n/sourcesdump/2006/0328/plan9/sys/src/cmd/tweak.c:536,541 - 
	/n/sourcesdump/2006/0329/plan9/sys/src/cmd/tweak.c:536,542
	  		return 10 + (c - 'a');
	  	if('A'<=c && c<='F')
	  		return 10 + (c - 'A');
	+ 	return 0;
	  }
	  
	  Thing*