Create Array..., "Use first free number" dependent on Pad numbering start

[Thomas Pointhuber]

# Current Behaviour

footprint editor -> click on pad -> "Create Array..."

1. select "From start value"
2. set start to 'A'
3. select "Use first free number"
4. Press OK

Script says it cannot determine numbering. The field is greyed out and should not be used anyway.

# Expected behaviour

do not use greyed-out fields inside tool

# Version Information

Application: kicad
Version: (5.1.0-rc1-2-g507229809), debug build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.63.0 OpenSSL/1.1.1a zlib/1.2.11 libidn2/2.1.0 libpsl/0.20.2 (+libidn2/2.1.0) libssh2/1.8.0 nghttp2/1.35.1
Platform: Linux 4.20.6-arch1-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.69.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.63.0
    Compiler: Clang 7.0.1 with C++ ABI 1002

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

[KiCad Janitor (kicad-janitor)]

Fixed in revision edc73de023b4f080664b1dc1291458928da3eb8a
https://git.launchpad.net/kicad/patch/?id=edc73de023b4f080664b1dc1291458928da3eb8a