Fix of "Use of uninitialized value $t in substitution"

[jazzl0ver]

Following command issues multiple errors:

/usr/bin/cfgmaker --global "forks: 2" --global "HtmlDir: /var/www/mrtg" --global "ImageDir: /var/www/mrtg"     --global "LogDir: /var/lib/mrtg" --global "ThreshDir: /var/lib/mrtg" --global "Options[_]: growright,bits"     --global "LogFormat: rrdtool" --global "IconDir: /mrtg" --subdirs=HOSTNAME     --if-filter='$default && ($if_type != 53)' --ifref=name --ifdesc=alias public@sw-4
Use of uninitialized value $t in substitution (s///) at /usr/bin/cfgmaker line 1376.
Use of uninitialized value $t in substitution (s///) at /usr/bin/cfgmaker line 1377.
Use of uninitialized value $t in substitution (s///) at /usr/bin/cfgmaker line 1378.
Use of uninitialized value $fs in pattern match (m//) at /usr/bin/cfgmaker line 1383.
Use of uninitialized value $t in hash element at /usr/bin/cfgmaker line 1384.
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