Patch fix for #1360 until WriteStream (#780) can be implemented.

src/cascadia/TerminalCore/Terminal.cpp

@@ -381,6 +381,18 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             }
         }
 
+        // If we're about to try to place the cursor past the right edge of the buffer, move it down a row
+        // This is another patch that GH#780 should supercede. This is really correcting for other bad situations
+        // like bisecting (writing only the leading half because there's no room for the trailing) a wide character
+        // into the buffer. However, it's not really all-up correctable without implementing a full WriteStream here.
+        // Also, this particular code RIGHT HERE shouldn't need to know anything about the cursor or the cells advanced
+        // which also will be solved by GH#780 (hopefully).
+        if (proposedCursorPosition.X > bufferSize.RightInclusive())
+        {
+            proposedCursorPosition.X = 0;
+            proposedCursorPosition.Y++;
+        }
+
         // If we're about to scroll past the bottom of the buffer, instead cycle the buffer.
         const auto newRows = proposedCursorPosition.Y - bufferSize.Height() + 1;
         if (newRows > 0)