Reset command, width and modified for %n and %t in from_stream.

date.h

@@ -5805,6 +5805,9 @@ from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
                     for (++fmt; *fmt == 'n' || *fmt == 't'; ++fmt)
                         ;
                     --fmt;
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
                 }
                 else
                     read(is, *fmt);

test/date_test/parse.pass.cpp

@@ -728,6 +728,18 @@ test_trailing_Z()
     assert(input.eof());
 }
 
+void
+test_leading_ws()
+{
+    using namespace std;
+    using namespace date;
+    istringstream in{"05/04/17 5/4/17"};
+    year_month_day d1, d2;
+    in >> parse("%D", d1) >> parse("%n%D", d2);
+    assert(d1 == may/4/2017);
+    assert(d2 == may/4/2017);
+}
+
 int
 main()
 {
@@ -756,4 +768,5 @@ main()
     test_z();
     test_Z();
     test_trailing_Z();
+    test_leading_ws();
 }