deal with empty lines in input file (fix #15)

dnseval.py

@@ -34,9 +34,9 @@ import sys
 import time
 from statistics import stdev
 
+import dns.flags
 import dns.rdatatype
 import dns.resolver
-import dns.flags
 
 __VERSION__ = 1.0
 __PROGNAME__ = os.path.basename(sys.argv[0])
@@ -179,6 +179,9 @@ def main():
         print((70 + width) * '-')
         for server in f:
             # check if we have a valid dns server address
+            if server.lstrip() == '':  # deal with empty lines
+                continue
+
             try:
                 ipaddress.ip_address(server)
             except ValueError:  # so it is not a valid IPv4 or IPv6 address, so try to resolve host name