Cppcheck: make 1-argument ctors explicit

Change-Id: I437988b238af961c6a3ac61ed4e93ea8206f6001
Reviewed-on: https://gerrit.libreoffice.org/60123
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

framework/inc/helper/shareablemutex.hxx

@@ -70,7 +70,7 @@ class FWI_DLLPUBLIC ShareableMutex
 class ShareGuard
 {
     public:
-        ShareGuard( ShareableMutex& rShareMutex ) :
+        explicit ShareGuard( ShareableMutex& rShareMutex ) :
             m_rShareMutex( rShareMutex )
         {
             m_rShareMutex.acquire();