bridging: Fix empty string test (on static allocation)

bridging: Fix empty string test (on static allocation)

Observed issue using clang on GNU/Linux:

  bridging/common/pluginServer.cpp:211:14:\
  error: comparison of array 'ctx->reconnect_file_name' \
  not equal to a null pointer is always true \
  [-Werror,-Wtautological-pointer-compare]
  if (ctx->reconnect_file_name != NULL)

Change-Id: Ifc5e40ba8d7943ca648e93627ed77cbc25f2731a
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18369
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-by: Todd Malsbary <todd.malsbary@intel.com>
(cherry picked from commit 995c584afef7af741d32fc024366d245fa2cf1ca)
Reviewed-on: https://gerrit.iotivity.org/gerrit/19129
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Tested-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>