opal/dss: silence coverity issues

CID 1269988 Use after free (USE_AFTER_FREE)
CID 1269987 Use after free (USE_AFTER_FREE)

Both are false positives as convert is always overwritten by the call
to opal_dss_unpack_string(). Set convert to prevent this issue from
re-appearing.

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

opal/dss/dss_unpack.c

@@ -1,3 +1,4 @@
+/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil -*- */
 /*
  * Copyright (c) 2004-2007 The Trustees of Indiana University and Indiana
  *                         University Research and Technology
@@ -9,7 +10,7 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
- * Copyright (c) 2012      Los Alamos National Security, Inc.  All rights reserved. 
+ * Copyright (c) 2012-2015 Los Alamos National Security, Inc.  All rights reserved.
  * Copyright (c) 2014      Intel, Inc. All rights reserved.
  * Copyright (c) 2014-2015 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
@@ -430,6 +431,7 @@ int opal_dss_unpack_float(opal_buffer_t *buffer, void *dest,
         tmp = strtof(convert, NULL);
         memcpy(&desttmp[i], &tmp, sizeof(tmp));
         free(convert);
+        convert = NULL;
     }
     return OPAL_SUCCESS;
 }
@@ -460,6 +462,7 @@ int opal_dss_unpack_double(opal_buffer_t *buffer, void *dest,
         tmp = strtod(convert, NULL);
         memcpy(&desttmp[i], &tmp, sizeof(tmp));
         free(convert);
+        convert = NULL;
     }
     return OPAL_SUCCESS;
 }