Recover input filename from symlink on error message

The recent commit to accept files from stdin broken the feature of
returning the input filename on an error, returning the temp filename
instead, which is confusing.

ocrmypdf/main.py

@@ -366,14 +366,16 @@ def re_symlink(input_file, soft_link_name, log=_log):
     if os.path.lexists(soft_link_name):
         # do not delete or overwrite real (non-soft link) file
         if not os.path.islink(soft_link_name):
-            raise Exception("%s exists and is not a link" % soft_link_name)
+            raise FileExistsError(
+                "%s exists and is not a link" % soft_link_name)
         try:
             os.unlink(soft_link_name)
         except:
             log.debug("Can't unlink %s" % (soft_link_name))
 
     if not os.path.exists(input_file):
-        raise Exception("trying to create a broken symlink to %s" % input_file)
+        raise FileNotFoundError(
+            "trying to create a broken symlink to %s" % input_file)
 
     log.debug("os.symlink(%s, %s)" % (input_file, soft_link_name))
 
@@ -409,7 +411,16 @@ def triage_image_file(input_file, output_file, log):
         log.info("Input file is not a PDF, checking if it is an image...")
         im = Image.open(input_file)
     except EnvironmentError as e:
-        log.error(e)
+        msg = str(e)
+
+        # Recover the original filename
+        realpath = ''
+        if os.path.islink(input_file):
+            realpath = os.path.realpath(input_file)
+        elif os.path.isfile(input_file):
+            realpath = '<stdin>'
+        msg = msg.replace(input_file, realpath)
+        log.error(msg)
         sys.exit(ExitCode.input_file)
         return
     else:
@@ -1323,7 +1334,11 @@ def run_pipeline():
                 from shutil import copyfileobj
                 copyfileobj(sys.stdin.buffer, stream_buffer)
         else:
-            re_symlink(options.input_file, start_input_file, _log)
+            try:
+                re_symlink(options.input_file, start_input_file, _log)
+            except FileNotFoundError:
+                _log.error("File not found - " + options.input_file)
+                return ExitCode.input_file
 
         cmdline.run(options)
     except ruffus_exceptions.RethrownJobError as e: