CamelPOP3Folder: Fix a potential g_object_unref(NULL) call

If all the branch conditions in this function evaluate to FALSE, the
stream is never set, and hence g_object_unref(NULL) is called on exiting
the function.

Found by scan-build.

https://bugzilla.gnome.org/719533

(cherry picked from commit 1161f3fbc1f6018fbc163b2f3078c5938f983c19)
EBookBackendCache: Remove an unnecessary NULL check.

A newly-created EContact is never NULL, so the check is redundant.
It was confusing the static analyser.

https://bugzilla.gnome.org/719533

(cherry picked from commit 047c4470a554c6f4e9a5a83b414d2d65ef759436)
libecal: Refactor system timezone key file parsing code

Previously, the code could call g_strstrip(NULL) if a line started with
a quotation mark but didn’t end with one, e.g.:
    MyKey="some-unbalanced-value

The code now ignores unbalanced quotation marks, returning the odd one
in the value rather than crashing (or stripping it).

Found by scan-build.

https://bugzilla.gnome.org/719533

(cherry picked from commit f851d77bcec88d4a2e664185ba760f9cfd08ee1f)
libedata-cal: Fix a potential g_strstrip(NULL) call

If the calendar contained any attendees _not_ prefixed with ‘mailto:’,
the text variable would be NULL, and would cause an assertion failure in
g_strstrip().

Found by scan-build.

https://bugzilla.gnome.org/719533

(cherry picked from commit 3304de4e2db1be25fb40a413e824b6c0f44069a9)
tests: Fix potential g_object_unref(NULL) calls in libebook tests

Found by scan-build.

https://bugzilla.gnome.org/719533

(cherry picked from commit fcccd30fb3d34feb2b040bade6c0595314e4e4e5)