make fails in case of network but no internet

[dewagter]

Error: integer expected in '' bij BUILD messages.h

Although it was not instantly obvious from the error description, according to strace this error seems to be caused by a combination of 2 paparazzi features:

1. in some cases with a bad mobile internet connection conf/maps.xml is built but has an empty google_version=""
2. gen_messages.xml needs to open maps.xml before it even starts gen_messages.ml when run from gen_messages.out script.

[dewagter]

Exception: Failure "Error: integer expected in ''".
make: *** [/home/mavlab/paparazzi/var/include/messages.h] Error 2

related: #65
related: #64

reconstruct the problem:

a) go near a hotspot but do not login of unplug the internet cable of your Wireless router (so you have an ip but no internet)
b) make

in data/maps/makefile:

is there a way to detect if grep found nothing and then put the example number instead ?

$(Q)echo "<maps google_version=""grep -P "http://khm[0-9]+.google.com/kh/v=[0-9]+.x26" $(DATADIR)/maps.google.com | sed -E s#.*http://khm[0-9]+.google.com/kh/v=## | sed -E s#.x26.*##""/>" >> $(@)