[XrdPosix] Fix Clang -Wtautological-constant-out-of-range-compare war…

…ning

src/XrdPosix/XrdPosixAdmin.cc:71:10: warning: result of comparison of constant
32940614417338485 with expression of type 'unsigned int' is always false
[-Wtautological-constant-out-of-range-compare]

   if (i > std::numeric_limits<ptrdiff_t>::max() / sizeof(XrdCl::URL))
       ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here std::numeric_limits<ptrdiff_t>::max() / sizeof(XrdCl::URL) == 32940614417338485,
which is bigger than the largest unsigned int, therefore the
comparison will always be false. We need i to be able to hold large
enough values. Fixes 0dc292f.

src/XrdPosix/XrdPosixAdmin.cc

@@ -51,7 +51,7 @@ XrdCl::URL *XrdPosixAdmin::FanOut(int &num)
    XrdCl::URL                    *uVec;
    XrdNetAddr netLoc;
    const char *hName;
-   unsigned int i;
+   unsigned long i;
 
 // Make sure admin is ok
 //