Fix Array `safeValue(at:)`

Array extension safaValue(at:) method would crash if a negative index is used.

CardParts/CardParts/src/Extensions/Array.swift

Lines 11 to 17 in 3234eda

    
           func safeValue(at index: Int) -> Element? { 
        
               if index < self.count { 
        
                   return self[index] 
        
               } else { 
        
                   return nil 
        
               } 
        
           }

Though it does not introduce any bug at present as there is only one occurrence of safeValue usage, in CardPartHistogramView, which does not use a negative index, the extension method would crash if a negative index is used.

CardParts/CardParts/src/Classes/Card Parts/CardPartHistogramView.swift

Lines 83 to 85 in 27126a7

    
           for (index, entry) in barEntries.enumerated() { 
        
               showEntry(index: index, entry: entry, animated: animated, oldEntry: oldValue.safeValue(at: index)) 
        
           }

Could we add a add a check for negative value to ensure that method work for all index values.
(fix available in branch: https://github.com/mak-s/CardParts/tree/array_index_out_of_range)

Also, CardParts code coverage is less. I'd like to add some Unit tests for existing classes available in CardParts.

Could you please let me know if I should create a new Issue for adding Unit tests.

	func safeValue(at index: Int) -> Element? {
	if index < self.count {
	return self[index]
	} else {
	return nil
	}
	}

	for (index, entry) in barEntries.enumerated() {
	showEntry(index: index, entry: entry, animated: animated, oldEntry: oldValue.safeValue(at: index))
	}