Ignore some extra string arguments to ShowMap (Fixes #2029)

Required for a dialogue result script in Morrowind.esm ("ShowMap Dren Plantation").
This must do the same as "ShowMap Dren", which actually does work properly, since ShowMap supports partial string matching.

components/compiler/extensions0.cpp

@@ -226,7 +226,7 @@ namespace Compiler
             extensions.registerInstruction ("togglefullhelp", "", opcodeToggleFullHelp);
             extensions.registerInstruction ("tfh", "", opcodeToggleFullHelp);
 
-            extensions.registerInstruction ("showmap", "S", opcodeShowMap);
+            extensions.registerInstruction ("showmap", "Sxxxx", opcodeShowMap);
             extensions.registerInstruction ("fillmap", "", opcodeFillMap);
             extensions.registerInstruction ("menutest", "/l", opcodeMenuTest);
             extensions.registerInstruction ("togglemenus", "", opcodeToggleMenus);