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: