findinfiles: Skip empty strings when building file pattern regexp

When building the regexp for file patterns when exclude_re is
false, skip empty strings.

This fixes issue spyder-ide#7811 when exclude_re is false.

spyder/widgets/findinfiles.py

@@ -561,7 +561,8 @@ def get_options(self, all=False):
 
         if not exclude_re:
             items = [fnmatch.translate(item.strip())
-                     for item in exclude.split(",")]
+                     for item in exclude.split(",")
+                     if item.strip() != '']
             exclude = '|'.join(items)
 
         # Validate regular expressions:

spyder/widgets/tests/test_findinfiles.py

@@ -157,6 +157,18 @@ def test_exclude_extension_empty_regex(qtbot):
     assert expected_results() == matches
 
 
+def test_exclude_extension_string(qtbot):
+    find_in_files = setup_findinfiles(qtbot, exclude="",
+                                      exclude_regexp=False)
+    find_in_files.set_search_text("spam")
+    find_in_files.find_options.set_directory(osp.join(LOCATION, "data"))
+    find_in_files.find()
+    blocker = qtbot.waitSignal(find_in_files.sig_finished)
+    blocker.wait()
+    matches = process_search_results(find_in_files.result_browser.data)
+    assert expected_results() == matches
+
+
 def test_exclude_extension_multiple_string(qtbot):
     find_in_files = setup_findinfiles(qtbot, exclude="*.py, *.cpp",
                                       exclude_regexp=False)