Fix uninitialized values in require.c

This was reported running cppcheck over require's code.
require-ess/src/require.c:1002:33: error: Uninitialized variable: &modulediroffs [uninitvar]
               dirname, module, &modulediroffs);
                                ^
require-ess/src/require.c:996:18: note: Assuming condition is false
      if (dirlen == 0) continue; /* ignore empty driverpath elements */
                 ^
require-ess/src/require.c:1002:33: note: Uninitialized variable: &modulediroffs
               dirname, module, &modulediroffs);
                                ^

require-ess/src/require.c

@@ -981,8 +981,8 @@ static int require_priv(
     /* Search for module in driverpath */
     for (dirname = driverpath; dirname != NULL; dirname = end) {
       /* get one directory from driverpath */
-      int dirlen;
-      int modulediroffs;
+      int dirlen = 0;
+      int modulediroffs = 0;
       DIR_HANDLE dir;
       DIR_ENTRY direntry;