kivy: fix can_pay in invoice_dialog
kivy: fix can_pay in invoice_dialog

pooler/electrum-ltc,pooler/electrum-ltc,vialectrum/vialectrum,pooler/electrum-ltc,vialectrum/vialectrum,vialectrum/vialectrum,wakiyamap/electrum-mona,spesmilo/electrum,pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona,spesmilo/electrum,wakiyamap/electrum-mona,spesmilo/electrum,wakiyamap/electrum-mona