pv: use unsigned for safer non-ascii bit shifting for hexa

- related to GH #2690

(cherry picked from commit c331e6dddb238abe5fc832ce3d3934fbe56ad2f7)

src/modules/pv/pv_core.c

@@ -615,20 +615,22 @@ int pv_get_flag(struct sip_msg *msg, pv_param_t *param,
 	return pv_get_uintval(msg, param, res, (msg->flags & (1<<param->pvn.u.isname.name.n)) ? 1 : 0);
 }
 
-static inline char* int_to_8hex(int val)
+static inline char* int_to_8hex(int sval)
 {
 	unsigned short digit;
 	int i;
 	static char outbuf[9];
+	unsigned int uval;
 
+	uval = (unsigned int)sval;
 	outbuf[8] = '\0';
 	for(i=0; i<8; i++)
 	{
-		if(val!=0)
+		if(uval!=0)
 		{
-			digit =  val & 0x0f;
+			digit =  uval & 0x0f;
 			outbuf[7-i] = digit >= 10 ? digit + 'a' - 10 : digit + '0';
-			val >>= 4;
+			uval >>= 4;
 		}
 		else
 			outbuf[7-i] = '0';

src/modules/pv/pv_trans.c

@@ -118,7 +118,7 @@ static int pdu_7bit_encode(str sin) {
 	nleft = 1;
 	j = 0;
 	for(i = 0; i < sin.len; i++) {
-		hex = *(sin.s) >> (nleft - 1);
+		hex = (unsigned char)(*(sin.s)) >> (nleft - 1);
 		fill = *(sin.s+1) << (8-nleft);
 		hex = hex | fill;
 		_tr_buffer[j++] = HexTbl[hex >> 4];
@@ -292,7 +292,7 @@ int tr_eval_string(struct sip_msg *msg, tr_param_t *tp, int subtype,
 			j = 0;
 			for(i=0; i<val->rs.len; i++)
 			{
-				_tr_buffer[j++] = fourbits2char[val->rs.s[i] >> 4];
+				_tr_buffer[j++] = fourbits2char[(unsigned char)val->rs.s[i] >> 4];
 				_tr_buffer[j++] = fourbits2char[val->rs.s[i] & 0xf];
 			}
 			_tr_buffer[j] = '\0';