[gparted] Improve comment about disallowing shrinking when the FS usage is unknown

[Curtis Gedak <gedakc src gnome org>]

commit 8373d36ed26b110bd11b04fc354f6bee49dfb9b5
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Nov 12 13:20:22 2016 +0000

    Improve comment about disallowing shrinking when the FS usage is unknown
    
    Explain when and why shrinking file systems is disallowed.
    
    Unnecessary history.  Check added in 2004-12-15:
        d100935b55d44786c41f85f1c88bc7bdf14f2221
        :Set_Valid_Operations()
    
    Comment later added in 2006-07-30:
        677a21f50ade33dcd19e3438d63d5db53182db37
        improved errorhandling a bit. At the initialscan we store errors/warnings

 src/Dialog_Partition_Resize_Move.cc |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/Dialog_Partition_Resize_Move.cc b/src/Dialog_Partition_Resize_Move.cc
index 40723b1..2dea1f2 100644
--- a/src/Dialog_Partition_Resize_Move.cc
+++ b/src/Dialog_Partition_Resize_Move.cc
@@ -74,7 +74,8 @@ void Dialog_Partition_Resize_Move::Resize_Move_Normal( const PartitionVector & p
 {
        g_assert( new_partition != NULL );  // Bug: Not initialised by constructor calling set_data()
 
-       //little bit of paranoia ;)
+       // Don't permit shrinking an existing file system (other than linux-swap) when the
+       // usage is unknown as that sets the minimum resize.
        if ( ! new_partition->sector_usage_known()      &&
             new_partition->status     != STAT_NEW      &&
             new_partition->filesystem != FS_LINUX_SWAP    )