minor tweaks

R=r
DELTA=9  (2 added, 5 deleted, 2 changed)
OCL=24107
CL=24152

src/runtime/iface.c

@@ -178,13 +178,8 @@ throw:
 			sname = st[nt].name;
 			if(sname == nil) {
 				if(!canfail) {
-					prints("cannot convert type ");
-					prints((int8*)st[0].name);
-					prints(" to interface ");
-					prints((int8*)si[0].name);
-					prints(": missing method ");
-					prints((int8*)iname);
-					prints("\n");
+					printf("cannot convert type %s to interface %s: missing method %s\n",
+						st[0].name, si[0].name, iname);
 					if(iface_debug) {
 						prints("interface");
 						printsigi(si);

src/runtime/string.c

@@ -12,6 +12,8 @@ findnull(byte *s)
 {
 	int32 l;
 
+	if(s == nil)
+		return 0;
 	for(l=0; s[l]!=0; l++)
 		;
 	return l;