Don't raise OSError from memFileInput()

faststreams/inputs.nim

@@ -166,7 +166,7 @@ let memFileInputVTable = InputStreamVTable(
 )
 
 proc memFileInput*(filename: string, mappedSize = -1, offset = 0): InputStreamHandle
-                  {.raises: [IOError, OSError].} =
+                  {.raises: [IOError].} =
   ## Creates an input stream for reading the contents of a memory-mapped file.
   ##
   ## Using this API will provide better performance than `fileInput`,
@@ -187,6 +187,7 @@ proc memFileInput*(filename: string, mappedSize = -1, offset = 0): InputStreamHa
   # Nim's memfiles module will fail to map an empty file,
   # but we don't consider this a problem. The stream will
   # be in non-readable state from the start.
+  try:
     let fileSize = getFileSize(filename)
     if fileSize == 0:
       return makeHandle InputStream()
@@ -205,6 +206,8 @@ proc memFileInput*(filename: string, mappedSize = -1, offset = 0): InputStreamHa
         startAddr: head,
         endAddr: offset(head, mappedSize)),
       file: memFile)
+  except OSError as err:
+    raise newException(IOError, err.msg, err)
 
 func getNewSpan(s: InputStream) =
   let buffers = s.buffers