[gparted] Fix NULL == 0 assumption in call to ped_partition_flag_next() (!100)

[Mike Fleetwood <mfleetwo src gnome org>]

commit 3d4b1c1e7b33f229efd254fb0cc06660af627ea0
Author: Dominika Liberda <ja sdomi pl>
Date:   Sun Apr 10 21:09:56 2022 +0200

    Fix NULL == 0 assumption in call to ped_partition_flag_next() (!100)
    
    GParted fails to build on Alpine Linux Edge (development tree for the
    next release) like this:
    
        GParted_Core.cc: In constructor 'GParted::GParted_Core::GParted_Core()':
        GParted_Core.cc:75:64: error: invalid 'static_cast' from type 'std::nullptr_t' to type 
'PedPartitionFlag'
           75 |     for ( PedPartitionFlag flag = ped_partition_flag_next( static_cast<PedPartitionFlag>( 
NULL ) ) ;
              |                                                            
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    
    The code is failing to compile now because musl libc 1.2.3 has became
    more C++11 strict [1][2] by defining NULL [3] as nullptr [4] rather than
    as 0.  The parameter to ped_partition_flag_next() [5] should always have
    been numeral 0 cast to an enumeration and never the NULL pointer.
    
    Fixes this commit [6] from 2004-12-27 which changed the parameter from 0
    to NULL.
    
    [1] define NULL as nullptr when used in C++11 or later
        https://git.musl-libc.org/cgit/musl/commit?id=98e688a9da5e7b2925dda17a2d6820dddf1fb28
    [2] NULL vs nullptr (Why was it replaced?) [duplicate]
        https://stackoverflow.com/questions/20509734/null-vs-nullptr-why-was-it-replaced
    [3] C++ reference, NULL
        https://en.cppreference.com/w/cpp/types/NULL
    [4] C++ reference, nullptr
        https://en.cppreference.com/w/cpp/language/nullptr
    [5] libparted Documentation, ped_partition_flag_next()
        https://www.gnu.org/software/parted/api/group__PedPartition.html#g0ce9ce4247b320011bc8e9d957c8cdbb
    [6] Added cylsize to Device and made Operation contain a Device instead
        commit 174f0cff77c5799a713954a22b2c54306d03036c
    
    Closes !100 - Fix NULL == 0 assumption in call to
                  ped_partition_flag_next()

 src/GParted_Core.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
index 46c65193..603563c4 100644
--- a/src/GParted_Core.cc
+++ b/src/GParted_Core.cc
@@ -72,7 +72,7 @@ GParted_Core::GParted_Core()
        ped_exception_set_handler( ped_exception_handler ) ; 
 
        //get valid flags ...
-       for ( PedPartitionFlag flag = ped_partition_flag_next( static_cast<PedPartitionFlag>( NULL ) ) ;
+       for ( PedPartitionFlag flag = ped_partition_flag_next( static_cast<PedPartitionFlag>( 0 ) ) ;
              flag ;
              flag = ped_partition_flag_next( flag ) )
                flags .push_back( flag ) ;