Fix #7239, Stack overflow when calling create_directories(":D"). The reported problem was a symptom of an internal bug that caused path::filename() and path::parent_path() to fail on Windows for path(":"), and that in turn caused other functions that depend on filename() or parent_path() to fail, such as create_directories().

[SVN r80279]

src/operations.cpp

@@ -927,6 +927,7 @@ namespace detail
     }
 
     path parent = p.parent_path();
+    BOOST_ASSERT_MSG(parent != p, "internal error: p == p.parent_path()");
     if (!parent.empty())
     {
       // determine if the parent exists

src/path.cpp

@@ -510,7 +510,7 @@ namespace
     size_type pos(str.find_last_of(separators, end_pos-1));
 
 #   ifdef BOOST_WINDOWS_API
-    if (pos == string_type::npos)
+    if (pos == string_type::npos && end_pos > 1)
       pos = str.find_last_of(colon, end_pos-2);
 #   endif