[MSPAINT] Fix crash on zoom out

- Check the denominator for zero for both zoomed width and height.
- Do not allow to move zoom slider above possible position.
- Move commonly used `zoomTo` function into new header file.

CORE-14539

base/applications/mspaint/common.h

@@ -0,0 +1,14 @@
+/*
+ * PROJECT:     PAINT for ReactOS
+ * LICENSE:     LGPL
+ * FILE:        base/applications/mspaint/common.h
+ * PURPOSE:     Commonly used functions
+ * PROGRAMMERS: Benedikt Freisen
+ *              Stanislav Motylkov
+ */
+
+#pragma once
+
+/* FUNCTIONS ********************************************************/
+
+extern BOOL zoomTo(int, int, int);