Fix some crashes in diff and wrap map

Author: Nimaoth

src/text/diff_map.nim

@@ -152,6 +152,8 @@ proc `$`*(self: DiffMapSnapshot): string =
         inc i
 
 proc toDiffPoint*(self: DiffMapChunkCursor, point: InputPoint): DiffPoint =
+  if not (point.row in self.startPos.src...self.endPos.src):
+    return self.startPos.dst.diffPoint
   assert point.row in self.startPos.src...self.endPos.src
   # if self.startPos.dst == self.endPos.dst:
   #   return diffPoint(self.startPos.dst)

src/text/wrap_map.nim

@@ -678,17 +678,20 @@ proc next*(self: var WrapChunkIterator): Option[WrapChunk] =
     dst: self.wrapMapCursor.startPos.dst...self.wrapMapCursor.endPos.dst)
 
   if currentChunk.endOutputPoint <= map.src.b:
-    self.localOffset = currentChunk.len
+    self.localOffset = max(currentChunk.len, 0)
+    if self.localOffset < startOffset:
+      self.wrapChunk = WrapChunk(inputChunk: currentChunk, wrapPoint: self.wrapPoint).some
+      return self.wrapChunk
     assert self.localOffset >= 0
     var newChunk = currentChunk.split(startOffset).suffix.split(self.localOffset - startOffset).prefix
     newChunk.outputPoint = currentInputPoint
     self.wrapChunk = WrapChunk(inputChunk: newChunk, wrapPoint: self.wrapPoint).some
 
   else:
-    self.localOffset = map.src.b.column.int - currentChunk.outputPoint.column.int
-    if self.localOffset < 0:
+    self.localOffset = max(map.src.b.column.int - currentChunk.outputPoint.column.int, 0)
+    if self.localOffset < startOffset:
       self.wrapChunk = WrapChunk(inputChunk: currentChunk, wrapPoint: self.wrapPoint).some
-      return
+      return self.wrapChunk
 
     assert self.localOffset >= 0
     var newChunk = currentChunk.split(startOffset).suffix.split(self.localOffset - startOffset).prefix