builtin: fix string interpolation for autofree

vlib/v/gen/cgen.v

@@ -3054,7 +3054,7 @@ fn (mut g Gen) string_inter_literal(node ast.StringInterLiteral) {
 			// TODO: better check this case
 			g.write('${fmt}"PRId32"')
 		}
-		if i < node.exprs.len - 1 && !g.pref.autofree {
+		if i < node.exprs.len - 1 {
 			g.write('\\000')
 		}
 	}

vlib/v/gen/str.v

@@ -18,7 +18,7 @@ void _STR_PRINT_ARG(const char *fmt, char** refbufp, int *nbytes, int *memsize,
 			guess = vsnprintf(*refbufp + *nbytes, *memsize - *nbytes, fmt, args);
 			if (guess < *memsize - *nbytes) { // result did fit into buffer
 				*nbytes += guess;
-				return;
+				break;
 			}
 		}
 		// increase buffer (somewhat exponentially)