Windows: Fix buffer size of QueryInformationJobObject request

As noted in GHC #17926, the QueryInformationJobObject system call
apparently relies on the buffer size in addition to the
NumberOfAssignedProcesses field to determine how many results it should
return. For this reason it's important that we pass the true size of the
buffer to the call.

Author: bgamari

cbits/runProcess.c

@@ -862,8 +862,10 @@ waitForJobCompletion ( HANDLE hJob )
     JOBOBJECT_BASIC_PROCESS_ID_LIST *pid_list = NULL;
 
     while (true) {
+      size_t pid_list_size = sizeof(JOBOBJECT_BASIC_PROCESS_ID_LIST) + sizeof(ULONG_PTR) * (process_count - 1);
+
       if (pid_list == NULL) {
-        pid_list = malloc(sizeof(JOBOBJECT_BASIC_PROCESS_ID_LIST) + sizeof(ULONG_PTR) * process_count);
+        pid_list = malloc(pid_list_size);
         pid_list->NumberOfAssignedProcesses = process_count;
       }
 
@@ -872,7 +874,7 @@ waitForJobCompletion ( HANDLE hJob )
           hJob,
           JobObjectBasicProcessIdList,
           pid_list,
-          sizeof(JOBOBJECT_BASIC_PROCESS_ID_LIST),
+          pid_list_size,
           NULL);
 
       if (!success && GetLastError() == ERROR_MORE_DATA) {