Keep original field name

Author: FObermaier

src/NetTopologySuite.IO.Esri.Shapefile/Dbf/DbfStreamExtensions.cs

@@ -84,8 +84,7 @@ public static Encoding ReadDbfEncoding(this Stream stream)
         public static void WriteDbaseFieldDescriptor(this Stream stream, DbfField field, Encoding encoding)
         {
             encoding = encoding ?? Dbf.DefaultEncoding;
-            var name = field.Name.PadRight(Dbf.MaxFieldNameLength, char.MinValue); // Field name must have empty space zero-filled 
-
+            var name = field.OriginalName.PadRight(Dbf.MaxFieldNameLength, char.MinValue); // Field name must have empty space zero-filled 
 
             stream.WriteString(name, Dbf.MaxFieldNameLength, encoding);
             stream.WriteNullBytes(1);

src/NetTopologySuite.IO.Esri.Shapefile/Dbf/Fields/DbfField.cs

@@ -14,7 +14,12 @@ namespace NetTopologySuite.IO.Esri.Dbf.Fields
     public abstract class DbfField
     {
         // TODO: Spit DbfField into DbfFieldDefinition (Without Value property) and DbfFieldValue
-        private readonly string _name;
+
+        /// <summary>
+        /// Original field name
+        /// </summary>
+        internal string OriginalName { get; }
+
         /// <summary>
         /// Field Name.
         /// </summary>
@@ -23,7 +28,7 @@ public string Name
             get
             {
                 string suffix = DuplicateCount > 0 ? $"_{DuplicateCount}" : string.Empty;
-                return $"{_name}{suffix}";
+                return $"{OriginalName}{suffix}";
             }
         }
 
@@ -82,17 +87,12 @@ internal DbfField(string name, DbfType type, int length, int precision)
                 throw new ArgumentException($"Ivalid dBASE field precision: {precision}.", nameof(precision));
             }
 
-            _name = name;
+            OriginalName = name;
             FieldType = type;
             Length = length;
             NumericScale = precision;
         }
 
-        private bool IsValidFieldNameChar(char c)
-        {
-            return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || (c >= '0' && c <= '9');
-        }
-
         /// <inheritdoc/>
         public override string ToString()
         {