Rationalise null pointer checks in both decode_codepage functions, so

that decode_codepage(NULL) and decode_codepage("") both return the
default character set.

[originally from svn r9961]

unix/uxucs.c

@@ -265,7 +265,7 @@ const char *cp_enumerate(int index)
 
 int decode_codepage(char *cp_name)
 {
-    if (!*cp_name)
+    if (!cp_name || !*cp_name)
 	return CS_UTF8;
     return charset_from_localenc(cp_name);
 }

windows/winucs.c

@@ -1016,10 +1016,9 @@ int decode_codepage(char *cp_name)
     int codepage = -1;
     CPINFO cpinfo;
 
-    if (!*cp_name)
+    if (!cp_name || !*cp_name)
         return CP_UTF8;                /* default */
 
-    if (cp_name && *cp_name)
     for (cpi = cp_list; cpi->name; cpi++) {
         s = cp_name;
         d = cpi->name;
@@ -1047,7 +1046,6 @@ int decode_codepage(char *cp_name)
         }
     }
 
-    if (cp_name && *cp_name) {
     d = cp_name;
     if (tolower(d[0]) == 'c' && tolower(d[1]) == 'p')
         d += 2;
@@ -1064,7 +1062,6 @@ int decode_codepage(char *cp_name)
         codepage = GetOEMCP();
     if (codepage > 65535)
         codepage = -2;
-    }
 
   break_break:;
     if (codepage != -1) {