Fix octal validation loop index in GetScpFileMode

The upper-bound check in the octal-to-integer conversion loop used
modeOctet[0] instead of modeOctet[i], so only the first character
was validated against '7'. Characters at positions 1-3 could have
values above '7' without triggering an error.

src/wolfscp.c

@@ -854,7 +854,7 @@ static int GetScpFileMode(WOLFSSH* ssh, byte* buf, word32 bufSz,
 
     for (i = 0; i < SCP_MODE_OCTET_LEN; i++)
     {
-        if (modeOctet[i] < '0' || modeOctet[0] > '7') {
+        if (modeOctet[i] < '0' || modeOctet[i] > '7') {
             ret = WS_BAD_ARGUMENT;
             break;
         }