PowderPattern: update wavelength for FindPeaks

[vincefn]

In some cases, the wavelength is not correctly read during FindPeaks.
To be tested:

1. open powder pattern graph
2. change wavelength
3. search peaks
   if Powder pattern update is not updated, then the correct wavelength is not taken into account, despite WXCrystValidateAllUserInput()

Cannot reproduce in MacOs. Must test under windows.