only check for out of workspace in URL decode when it's necessary

src/url.c

@@ -133,16 +133,17 @@ url_decode(const enum encoding dec, char *restrict const buf,
 		while (*s && len) {
 			uint8_t nib2;
 
-			if (dest + 1 > end) {
-				errno = ENOMEM;
-				return -1;
-			}
 			switch(state) {
 			case NORMAL:
 				if (*s == '%')
 					state = PERCENT;
-				else
+				else {
+					if (dest == end) {
+						errno = ENOMEM;
+						return -1;
+					}
 					*dest++ = *s;
+				}
 				break;
 			case PERCENT:
 				if (isoutofrange(*s)
@@ -153,6 +154,10 @@ url_decode(const enum encoding dec, char *restrict const buf,
 				state = FIRSTNIB;
 				break;
 			case FIRSTNIB:
+				if (dest == end) {
+					errno = ENOMEM;
+					return -1;
+				}
 				if (isoutofrange(*s)
 				    || (nib2 = nibble[*s - '0']) == 0xff) {
 					errno = EINVAL;