Changed if/if/else/if/eleven chain to switch

Inlined isdigit in switch statement. Removed unused #includes.
Documented unreachable segment with code (Q_ASSERT).

Reviewed-by: Denis Dzyubenko
(cherry picked from commit 3596db6c9bb8db42476d0c7b52fa2043dc67135b)

Change-Id: I98c33801fd8794e95ba8fc0b5c4efe9b1910682b
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>

src/corelib/io/qtemporaryfile.cpp

@@ -53,10 +53,6 @@
 #  include <errno.h>
 #endif
 
-#include <stdlib.h>
-#include <time.h>
-#include <ctype.h>
-
 #if defined(Q_OS_UNIX)
 # include "private/qcore_unix_p.h"      // overrides QT_OPEN
 #endif
@@ -153,23 +149,34 @@ static int createFileFromTemplate(char *const path,
         for (char *iter = placeholderStart;;) {
             // Character progression: [0-9] => 'a' ... 'z' => 'A' .. 'Z'
             // String progression: "ZZaiC" => "aabiC"
-            if (*iter == 'Z') {
-                *iter++ = 'a';
-                if (iter == placeholderEnd)
-                    return -1;
-            } else {
-                if (isdigit(*iter))
+            switch (*iter) {
+                case 'Z':
+                    // Rollover, advance next character
                     *iter = 'a';
-                else if (*iter == 'z') /* inc from z to A */
+                    if (++iter == placeholderEnd)
+                        return -1;
+
+                    continue;
+
+                case '0': case '1': case '2': case '3': case '4':
+                case '5': case '6': case '7': case '8': case '9':
+                    *iter = 'a';
+                    break;
+
+                case 'z':
+                    // increment 'z' to 'A'
                     *iter = 'A';
-                else {
+                    break;
+
+                default:
                     ++*iter;
-                }
-                break;
+                    break;
             }
+            break;
         }
     }
-    /*NOTREACHED*/
+
+    Q_ASSERT(false);
 }
 
 //************* QTemporaryFileEngine