Nimpretty Fix negative indent breaks code (#13580)

changelog.md

@@ -126,6 +126,7 @@
 
 ### Tool changes
 
+- Fix Nimpretty must not accept negative indentation argument because breaks file.
 
 
 ### Compiler changes

nimpretty/nimpretty.nim

@@ -44,8 +44,8 @@ proc writeVersion() =
 
 type
   PrettyOptions = object
-    indWidth: int
-    maxLineLen: int
+    indWidth: Natural
+    maxLineLen: Positive
 
 proc prettyPrint(infile, outfile: string, opt: PrettyOptions) =
   var conf = newConfigRef()