tool_doswin: Fix uninitialized field warning

The partial struct initialization in 397664a0

 caused
a warning on uninitialized MODULEENTRY32 struct members:

  /src/tool_doswin.c:681:3: warning: missing initializer for field
  'th32ModuleID' of 'MODULEENTRY32 {aka struct tagMODULEENTRY32}'
  [-Wmissing-field-initializers]

This is sort of a bogus warning as the remaining members will be set
to zero by the compiler, as all omitted members are. Nevertheless,
remove the warning by omitting all members and setting the dwSize
members explicitly.

Closes #3254
Reviewed-by: Marcel Raad <Marcel.Raad@teamviewer.com>
Reviewed-by: Jay Satiro <raysatiro@yahoo.com>