SITELAT/SITELONG parsing error with PRISM (#1126) - V2

(V2) Allows a good parsing of these two keywords values in images from PRISM.

Also tested with :

• NINA
• INDI
• APT
• Sequence Generator
• TheSkyX
• Voyager
• MaximDL
• PRISM
• SharpCap

... to avoid any regression.

Should fix #1126 (closed)