fpg_tab: Refactored HandleLMousUp and extracted most of the code into a new
fpg_tab: Refactored HandleLMousUp and extracted most of the code into a new

method called TabSheetAtPos(). This allows the developer to reuse this
method too for other things.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI