[Enhancement] Password strength bar is visible even when the password text field is empty.

[Raunakk02]

Issue Description:
Currently, the password strength bar is visible to the user even when the password text field is empty.

Issue Severity:
Low
Environment Details:
Found in: talawa\lib\views\pages\login_signup\register_form.dart
Observed Behaviour:
The password strength bar is visible to the user even when the password text field is empty.
Expected Behaviour:
The password strength bar should only be visible if the password text field is not empty.
Are you willing to work on this issue:
I resolved the issue and submitted PR #392 Other information:
Linked to issue #210 some of which change has been somehow reverted.