testutils: Adapt to highly unlikely case

Coverity pointed out that getenv("PATH") may return NULL. Well,
we check for that in virFindFileInPath() too. If this happens, we
will pass NULL into strstr(). Ouch.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

tests/testutils.c

@@ -813,9 +813,16 @@ virTestSetEnvPath(void)
     const char *path = getenv("PATH");
     char *new_path = NULL;
 
-    if (strstr(path, abs_builddir) != path &&
-        (virAsprintf(&new_path, "%s:%s", abs_builddir, path) < 0 ||
-         setenv("PATH", new_path, 1) < 0))
+    if (path) {
+        if (strstr(path, abs_builddir) != path &&
+            virAsprintf(&new_path, "%s:%s", abs_builddir, path) < 0)
+            goto cleanup;
+    } else {
+        if (VIR_STRDUP(new_path, abs_builddir) < 0)
+            goto cleanup;
+    }
+
+    if (setenv("PATH", new_path, 1) < 0)
         goto cleanup;
 
     ret = 0;