Fix parser invalid index error that occurred when a field name was the same as an Excel function name. EPPlus treated the field name as a 'Function' even if the name was not followed by a left paranthesis to enclose the function arguments following the 'Function' name. We now treat the field name as a 'Name' rather than as a 'Function' when no left parathensis follows the field name. This is true even if the field name is the same as an Excel function name.

EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs

diff --git a/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs b/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
index a0d5d47..b8265a1 100644
--- a/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
+++ b/EPPlus/FormulaParsing/LexicalAnalysis/SourceCodeTokenizer.cs
@@ -217,6 +217,24 @@
                         token.TokenType = TokenType.NameValue;
                     }
                 }
+                else if (token.TokenType == TokenType.Function)
+                {
+                    if (i < context.Result.Count - 1)
+                    {
+                        if (context.Result[i + 1].TokenType == TokenType.OpeningParenthesis)
+                        {
+                            token.TokenType = TokenType.Function;
+                        }
+                        else
+                        {
+                            token.TokenType = TokenType.Unrecognized;
+                        }
+                    }
+                    else
+                    {
+                        token.TokenType = TokenType.Unrecognized;
+                    }
+                }
                 else if ((token.TokenType == TokenType.Operator || token.TokenType == TokenType.Negator) && i < context.Result.Count - 1 &&
                          (token.Value=="+" || token.Value=="-"))
                 {