Crash in JS_NewContext with low memory limit

[bnoordhuis]

Not super urgent but nice to fix.

Happens when the runtime memory limit is so low that the context cannot finish initializing. Requires many tedious tweaks to JS_NewContext and the JS_AddFeature helpers to handle out-of-memory conditions during their initialization steps.

Test:

diff --git a/api-test.c b/api-test.c
index 9bd3b63..84c99cd 100644
--- a/api-test.c
+++ b/api-test.c
@@ -631,6 +631,31 @@ static void global_object_prototype(void)
     }
 }
 
+static void low_memory_limit(void)
+{
+    unsigned base, limit;
+    JSRuntime *rt;
+    JSContext *ctx;
+    int all, ok;
+
+    all = ok = 0;
+    rt = JS_NewRuntime();
+    for (base = 512; base <= 64*1024; base = 2*base) {
+        for (limit = base; limit < 2*base; limit += base/8) {
+            JS_SetMemoryLimit(rt, limit);
+            ctx = JS_NewContext(rt); // expected to fail, not to crash
+            if (ctx) {
+                JS_FreeContext(ctx);
+                ok++;
+            }
+            all++;
+        }
+    }
+    JS_FreeRuntime(rt);
+    assert(ok > 0);     // expect some successes...
+    assert(ok < all);   // ...but not all
+}
+
 int main(void)
 {
     sync_call();
@@ -645,5 +670,6 @@ int main(void)
     dump_memory_usage();
     new_errors();
     global_object_prototype();
+    low_memory_limit();
     return 0;
 }

Example crash:

==3084694== Invalid write of size 8                                            
==3084694==    at 0x12506C: JS_NewObjectFromShape (quickjs.c:5043)
==3084694==    by 0x1252A6: JS_NewObjectProtoClass (quickjs.c:5119)
==3084694==    by 0x1C7A3F: JS_AddIntrinsicBasicObjects (quickjs.c:53423)      
==3084694==    by 0x11D26A: JS_NewContextRaw (quickjs.c:2374)                                                                                                  
==3084694==    by 0x11D2AF: JS_NewContext (quickjs.c:2383)                     
==3084694==    by 0x119C4C: small_memory_limit (api-test.c:646)                
==3084694==    by 0x119D40: main (api-test.c:673)                              
==3084694==  Address 0x0 is not stack'd, malloc'd or (recently) free'd