Server: fix unbound exception variable (#1051)

Author: dshemetov

src/server/_printer.py

@@ -58,7 +58,7 @@ def gen():
                     r = self._print_row(row)
                     if r is not None:
                         yield r
-            except:
+            except Exception as e:
                 get_structured_logger('server_error').error("Exception while executing printer", exception=e)
                 self.result = -1
                 yield self._error(e)