virISCSIGetSession: Don't leak memory

This function runs an iscsi command and parses its output.
However, due to the nature of things, virISCSIExtractSession()
callback can be called multiple times. In each run it would
allocate new memory and overwrite the variable where we keep
pointer to it and thus leaking old allocations.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
(cherry picked from commit 9c037c6c)

src/util/viriscsi.c

@@ -52,7 +52,8 @@ virISCSIExtractSession(char **const groups,
 {
     struct virISCSISessionData *data = opaque;
 
-    if (STREQ(groups[1], data->devpath))
+    if (!data->session &&
+        STREQ(groups[1], data->devpath))
         return VIR_STRDUP(data->session, groups[0]);
     return 0;
 }