Fix the sqlite3_mutex_alloc() interface to return NULL (not segfault) when

operating in threadsafe mode.  (This is a general-purpose bug fix which
really ought to be ported to trunk.)

FossilOrigin-Name: 64840a3caf569959c9d5e63bdbc0cf675fda3882

manifest

@@ -1,5 +1,8 @@
-C Add\stest\scase\sdemonstrating\sdeadlock\sduring\srecovery\sof\svery\slarge\slog\sfiles.\sNo\sfix\syet.
-D 2010-05-01T08:30:35
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA1
+
+C Fix\sthe\ssqlite3_mutex_alloc()\sinterface\sto\sreturn\sNULL\s(not\ssegfault)\swhen\noperating\sin\sthreadsafe\smode.\s\s(This\sis\sa\sgeneral-purpose\sbug\sfix\swhich\nreally\sought\sto\sbe\sported\sto\strunk.)
+D 2010-05-01T11:19:08
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@@ -139,7 +142,7 @@ F src/mem2.c 2ee7bdacda8299b5a91cff9f7ee3e46573195c38
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 F src/memjournal.c f3be374af30588de297dcf678925b2a4758e4135
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 F src/mutex.h 6fde601e55fa6c3fae768783c439797ab84c87c6
 F src/mutex_noop.c 5f58eaa31f2d742cb8957a747f7887ae98f16053
 F src/mutex_os2.c 20477db50cf3817c2f1cd3eb61e5c177e50231db
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manifest.uuid

@@ -1 +1 @@
-63ea318eb19d264667909c70185b8a5cdc4454c0
+64840a3caf569959c9d5e63bdbc0cf675fda3882

src/mutex.c

@@ -77,6 +77,7 @@ int sqlite3MutexEnd(void){
 ** Retrieve a pointer to a static mutex or allocate a new dynamic one.
 */
 sqlite3_mutex *sqlite3_mutex_alloc(int id){
+  if( !sqlite3GlobalConfig.bCoreMutex ) return 0;
 #ifndef SQLITE_OMIT_AUTOINIT
   if( sqlite3_initialize() ) return 0;
 #endif