Gerbview: Zoom do not work
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# Description
<!-- What is the current behavior and what is the expected behavior? -->
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Only 'Zoom to fit' works.

'Zoom in' shows smaller image.

Gerbview from version 5.1.6 works correctly.\
Git bisect showed commit 284d5861dd6da35373cefffe84c372bceb15b818 \
Reverting this commit resolved the issue.
# Steps to reproduce
<!-- If there are multiple steps to reproduce it or it is a visual issue, then providing a screen recording as an attachment to this report is recommended. -->
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1. Open gerber file. Eg. [lampC-LV-F_SilkS.gbr](/uploads/231f20fa116be57282eee9d96bd13ac0/lampC-LV-F_SilkS.gbr)
2. Press 'Zoom in'
# KiCad Version
```
Application: GerbView
Version: (5.1.8-8-g6223e7475), release build
Libraries:
wxWidgets 3.0.5
libcurl/7.73.0 OpenSSL/1.1.1h zlib/1.2.11 brotli/1.0.9 zstd/1.4.5 c-ares/1.16.1 libidn2/2.3.0 libpsl/0.21.1 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.41.0 librtmp/2.3
Platform: Linux 5.8.9 x86_64, 64 bit, Little endian, wxGTK
Build Info:
wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
Boost: 1.73.0
OpenCASCADE Community Edition: 6.9.1
Curl: 7.73.0
Compiler: GCC 10.2.0 with C++ ABI 1014
Build settings:
USE_WX_GRAPHICS_CONTEXT=OFF
USE_WX_OVERLAY=OFF
KICAD_SCRIPTING=ON
KICAD_SCRIPTING_MODULES=ON
KICAD_SCRIPTING_PYTHON3=OFF
KICAD_SCRIPTING_WXPYTHON=ON
KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
KICAD_SCRIPTING_ACTION_MENU=ON
BUILD_GITHUB_PLUGIN=ON
KICAD_USE_OCE=ON
KICAD_USE_OCC=OFF
KICAD_SPICE=ON
```
issue