fix: don't assume that successful weightFromArg links to valid index - #7084

Potential conflicts detected!

{ pull_number: 7084, conflictPrs: [ { number: 6833, files: [ 'doc/release-notes-6833.md', 'src/Makefile.qt.include', 'src/qt/addressbookpage.cpp', 'src/qt/addresstablemodel.cpp', 'src/qt/appearancewidget.cpp', 'src/qt/appearancewidget.h', 'src/qt/askpassphrasedialog.cpp', 'src/qt/bitcoin.cpp', 'src/qt/bitcoin.h', 'src/qt/bitcoingui.cpp', 'src/qt/coincontroldialog.cpp', 'src/qt/forms/appearancewidget.ui', 'src/qt/forms/optionsdialog.ui', 'src/qt/governancelist.cpp', 'src/qt/guiutil.cpp', 'src/qt/guiutil.h', 'src/qt/guiutil_font.cpp', 'src/qt/guiutil_font.h', 'src/qt/masternodelist.cpp', 'src/qt/modaloverlay.cpp', 'src/qt/openuridialog.cpp', 'src/qt/optionsdialog.cpp', 'src/qt/optionsmodel.cpp', 'src/qt/optionsmodel.h', 'src/qt/overviewpage.cpp', 'src/qt/overviewpage.h', 'src/qt/proposalwizard.cpp', 'src/qt/qrdialog.cpp', 'src/qt/qrimagewidget.cpp', 'src/qt/receivecoinsdialog.cpp', 'src/qt/receiverequestdialog.cpp', 'src/qt/rpcconsole.cpp', 'src/qt/sendcoinsdialog.cpp', 'src/qt/sendcoinsentry.cpp', 'src/qt/signverifymessagedialog.cpp', 'src/qt/splashscreen.cpp', 'src/qt/test/addressbooktests.cpp', 'src/qt/test/apptests.cpp', 'src/qt/test/optiontests.cpp', 'src/qt/test/optiontests.h', 'src/qt/test/test_main.cpp', 'src/qt/test/wallettests.cpp', 'src/qt/trafficgraphwidget.cpp', 'src/qt/transactiondescdialog.cpp', 'src/qt/utilitydialog.cpp', 'src/qt/walletview.cpp', 'test/util/data/non-backported.txt' ], conflicts: [ 'src/qt/optionsmodel.cpp' ] }, { number: 6831, files: [ 'src/qt/appearancewidget.cpp', 'src/qt/appearancewidget.h', 'src/qt/bitcoin.cpp', 'src/qt/forms/appearancewidget.ui', 'src/qt/guiutil.cpp', 'src/qt/guiutil.h', 'src/qt/guiutil_font.cpp', 'src/qt/guiutil_font.h', 'src/qt/optionsmodel.cpp', 'src/qt/optionsmodel.h', 'src/qt/overviewpage.cpp', 'src/qt/overviewpage.h' ], conflicts: [ 'src/qt/optionsmodel.cpp' ] } ] }