detect: fix scan-build warnings

detect-engine-address.c:1140:17: warning: Use of memory after it is freed [unix.Malloc]
            r = DetectAddressCmp(ag, ag2);
                ^~~~~~~~~~~~~~~~~~~~~~~~~
detect-engine-address.c:1169:17: warning: Use of memory after it is freed [unix.Malloc]
            r = DetectAddressCmp(ag, ag2);
                ^~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.

detect-engine-port.c:1161:9: warning: Use of memory after it is freed [unix.Malloc]
        DetectPortPrint(ag2);
        ^~~~~~~~~~~~~~~~~~~~
1 warning generated.

Bug: #3150.
Bug: #3151.

src/detect-engine-address.c

@@ -1140,14 +1140,12 @@ int DetectAddressMergeNot(DetectAddressHead *gh, DetectAddressHead *ghn)
             r = DetectAddressCmp(ag, ag2);
             /* XXX more ??? */
             if (r == ADDRESS_EQ || r == ADDRESS_EB) {
-                if (ag2->prev == NULL)
-                    gh->ipv4_head = ag2->next;
-                else
+                if (ag2->prev != NULL)
                     ag2->prev->next = ag2->next;
-
                 if (ag2->next != NULL)
                     ag2->next->prev = ag2->prev;
-
+                if (gh->ipv4_head == ag2)
+                    gh->ipv4_head = ag2->next;
                 /* store the next ptr and remove the group */
                 DetectAddress *next_ag2 = ag2->next;
                 DetectAddressFree(ag2);
@@ -1168,14 +1166,12 @@ int DetectAddressMergeNot(DetectAddressHead *gh, DetectAddressHead *ghn)
         for (ag2 = gh->ipv6_head; ag2 != NULL; ) {
             r = DetectAddressCmp(ag, ag2);
             if (r == ADDRESS_EQ || r == ADDRESS_EB) { /* XXX more ??? */
-                if (ag2->prev == NULL)
-                    gh->ipv6_head = ag2->next;
-                else
+                if (ag2->prev != NULL)
                     ag2->prev->next = ag2->next;
-
                 if (ag2->next != NULL)
                     ag2->next->prev = ag2->prev;
-
+                if (gh->ipv6_head == ag2)
+                    gh->ipv6_head = ag2->next;
                 /* store the next ptr and remove the group */
                 DetectAddress *next_ag2 = ag2->next;
                 DetectAddressFree(ag2);

src/detect-engine-port.c

@@ -1137,15 +1137,12 @@ static int DetectPortParseMergeNotPorts(const DetectEngineCtx *de_ctx,
 
             r = DetectPortCmp(ag, ag2);
             if (r == PORT_EQ || r == PORT_EB) { /* XXX more ??? */
-                if (ag2->prev == NULL) {
-                    *head = ag2->next;
-                } else {
+                if (ag2->prev != NULL)
                     ag2->prev->next = ag2->next;
-                }
-
-                if (ag2->next != NULL) {
+                if (ag2->next != NULL)
                     ag2->next->prev = ag2->prev;
-                }
+                if (*head == ag2)
+                    *head = ag2->next;
                 /** store the next ptr and remove the group */
                 DetectPort *next_ag2 = ag2->next;
                 DetectPortFree(de_ctx,ag2);