testing/firmware-samsung-manta: check that /etc/conf.d/wpa_supplicant exists (MR 3909)

Not all UIs depend on it

Fixes #1971

[ci:skip-build] already built successfully in CI

device/testing/firmware-samsung-manta/APKBUILD

@@ -1,6 +1,6 @@
 pkgname=firmware-samsung-manta
 pkgver=1
-pkgrel=0
+pkgrel=1
 pkgdesc="Firmware for Samsung Manta (Nexus 10)"
 url="https://developers.google.com/android/drivers#mantalmy49j"
 arch="armv7"

device/testing/firmware-samsung-manta/firmware-samsung-manta.post-install

@@ -5,6 +5,6 @@ rc-update -q add deferred-initcalls sysinit
 
 # Explicitly specify wlan device. Without this, p2p0 will be
 # selected automatically instead of wlan0, and Wi-Fi will not work.
-if ! grep -q "i wlan0" /etc/conf.d/wpa_supplicant ; then
+if [ -f /etc/conf.d/wpa_supplicant ] && ! grep -q "i wlan0" /etc/conf.d/wpa_supplicant ; then
 	sed -i 's/-Dnl80211,wext/-Dnl80211,wext -i wlan0/' /etc/conf.d/wpa_supplicant
 fi