external password backend does not work with special characters

[npiazza at disroot.org]

with a long password that contains special characters, the wpa_supplicant
can connect to the network if using

password="mypassword"

in the .config file (i.e. the actual password enclosed in quotation marks)
but not if using

password=ext:pwd_eduroam

with the external password file containing a line

pwd_eduroam=mypassword

without quotation marks.  I also tried and failed with quotation marks

pwd_eduroam="mypassword"

The external file works correctly with other networks, or simpler/shorter
passwords on this network.

Are there any restrictions on the characters allowed in the external file
backend, compared to the regular .conf file, or am I doing something wrong,
or missing some recently added patch?

Thanks.