hwdb: fix dangling 'else' ambuguity

Imagine the following use of hwdb:

    if (condition_A)
        SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value)
            operation_A(key, value);
    else
        log_error("...");

This should work just fine, but but definitely does not what you would
expect. Due to how SD_HWDB_FOREACH_PROPERTY is defined, the dangling
'else' is linked to the hidden 'if' statement in the macro instead of the
outer 'if (condition_A)'. This is unexpected and really annoying to debug.

Fix this by never leaving un-finished if-statements in
SD_HWDB_FOREACH_PROPERTY(). We simply inverse the if() statement and
explicitly add an 'else'-branch. This way, the statement is closed and all
ambuguities are resolved.
journal: fix dangling 'else' ambiguity

Rework the sd-journal iterators to avoid dangling 'else' ambiguity. For a
detailed explanation, see:

    commit bff686e2a981ccd0888cdf1981977d24320f1770
    Author: David Herrmann <dh.herrmann@gmail.com>
    Date:   Fri Dec 12 09:43:54 2014 +0100

        hwdb: fix dangling 'else' ambuguity