[BUGFIX] Default behaviour for field rendering of configuration is dropped

In TYPO3 4.7 (and below) the default field of a configuration was a text
field. With a wrong configuration type in ext_conf_template.txt now the
field isn't rendered any more. There should be a fallback to a normal
input field like it used to.

Fixes: #43042
Releases: 6.0

Change-Id: Ic49c9b19a7f8f1795889f17ed5c1efa364dfd9b9
Reviewed-on: http://review.typo3.org/16503
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel