When parsing strings while converting formulas, ensure the opening and closing quote charcter match.

EPPlus/ExcelCellBase.cs

diff --git a/EPPlus/ExcelCellBase.cs b/EPPlus/ExcelCellBase.cs
index a6bbc1c..61f8b5f 100644
--- a/EPPlus/ExcelCellBase.cs
+++ b/EPPlus/ExcelCellBase.cs
@@ -120,6 +120,12 @@
                 char c = value[pos];
                 if (c == '"' || c=='\'')
                 {
+                    if (isText == true && prevTQ != c)
+                    {
+                        ret += c;
+                        continue;
+                    }
+
                     if (isText == false && part != "" && prevTQ==c)
                     {
                         ret += addressTranslator(part, row, col, rowIncr, colIncr);