Fix WiFi (ZX or DPP) QR code parsing to ignore leading spaces

Increase robustness of QR code parsing: while leading spaces aren't
expected (or allowed) they are observed in the wild and can be safely
ignored.

Bug: 292331368
Test: validated that QR code with scan is now parsed correctly
Test: atest WifiQrCodeTest
Change-Id: Ifff79870bea2ec9924f7b2e8100c2c01fd350846