TimePicker dummy value check works for first time only

[manpreetk3289]

In TimePicker as it don't allow the user to add alphabets and any garbage value but that works for first time only .If after first time we try to add the garbage value the value retains in the textbox .

[fbasso]

For information, it will be partly fixed if #3247 will be merged, as it will not be possible to enter garbage values.

In fact, this validation issue will remain, but for invalid numbers (as an example, try to enter 50 in the hours field twice to get the issue).