INPLACE with URL fails

[jonashoechst]

The image is downloaded correctly, but when setting the DEST_IMG the URL is used and the the build fails, because this is not a valid file path:

### INPLACE http://downloads.openwrt.org/releases/18.06.4/targets/brcm2708/bcm2710/openwrt-18.06.4-brcm2708-bcm2710-rpi-3-ext4-factory.img.gz
losetup: http://downloads.openwrt.org/releases/18.06.4/targets/brcm2708/bcm2710/openwrt-18.06.4-brcm2708-bcm2710-rpi-3-ext4-factory.img.gz: failed to set up loop device: No such file or directory
/pimod/modules/qemu.sh: line 25: QEMU_GUEST: unbound variable
failed to stat() ### Error: "http://downloads.openwrt.org/releases/18.06.4/targets/brcm2708/bcm2710/openwrt-18.06.4-brcm2708-bcm2710-rpi-3-ext4-factory.img.gz" returned 1, cleaning up...
/pimod/modules/qemu.sh: line 25: QEMU_GUEST: unbound variable
### Error: "http://downloads.openwrt.org/releases/18.06.4/targets/brcm2708/bcm2710/openwrt-18.06.4-brcm2708-bcm2710-rpi-3-ext4-factory.img.gz" returned 1, cleaning up...
/pimod/modules/qemu.sh: line 25: QEMU_GUEST: unbound variable

Suggestions:

• disable use of INPLACE and an URL
• download the file locally and work on the local copy (semantic-wise not really inplace)