XYCurve disconnect when deleting columns is not correctly

X Column case

Steps to reproduce

1. Create spreadsheet with 2 columns and generate data
2. Create curve from those 2 columns
3. Delete column assigned as xColumn
4. Change linetype in xycurve

Expected

Nothing crashes

Currently

Labplot crashes

Y Column case

Steps to reproduce

1. Create spreadsheet with 2 columns and generate data
2. Create curve from those 2 columns
3. Delete column assigned as yColumn
4. Change linetype in xycurve

Expected

Nothing changes

Currently

A curve is drawn. Maybe numberOfPoints gets not cleared

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Release build 2.9.0-592-gafd15ba16
Sep 19 2022, 04:31:19
System: Windows 10 Version 2009
Locale: German,Germany (Decimal point ',', Group separator '.')
Number settings: Decimal point '.', Group separator ',', Exponential 'e', Zero digit '0', Percent '%', Positive/Negative sign '+'/'-' (Updated on restart)
Architecture: x86_64-little_endian-llp64
Kernel: winnt 10.0.19043
C++ Compiler: MSVC 19.29.30038.1
C++ Compiler Flags: /DWIN32 /D_WINDOWS /W3 /GR /EHsc /wd4250 /wd4251 /wd4396 /wd4661 /Zc:__cplusplus -O2 -W3 -DPSAPI_VERSION=1