avoid truth-testing overhead in Py3.3+ also for non-ready (wchar_t) Unicode strings

Cython/Compiler/ExprNodes.py

@@ -12317,7 +12317,7 @@ class CoerceToBooleanNode(CoercionNode):
         Builtin.set_type:        'PySet_GET_SIZE',
         Builtin.frozenset_type:  'PySet_GET_SIZE',
         Builtin.bytes_type:      'PyBytes_GET_SIZE',
-        Builtin.unicode_type:    '__Pyx_PyUnicode_GET_LENGTH',
+        Builtin.unicode_type:    '__Pyx_PyUnicode_IS_TRUE',
     }
 
     def __init__(self, arg, env):

Cython/Utility/ModuleSetupCode.c

@@ -93,6 +93,7 @@
   #define __Pyx_PyUnicode_KIND(u)         PyUnicode_KIND(u)
   #define __Pyx_PyUnicode_DATA(u)         PyUnicode_DATA(u)
   #define __Pyx_PyUnicode_READ(k, d, i)   PyUnicode_READ(k, d, i)
+  #define __Pyx_PyUnicode_IS_TRUE(u)      (0 != (likely(PyUnicode_IS_READY(op)) ? PyUnicode_GET_LENGTH(u) : PyUnicode_GET_SIZE(u)))
 #else
   #define CYTHON_PEP393_ENABLED 0
   #define __Pyx_PyUnicode_READY(op)       (0)
@@ -102,6 +103,7 @@
   #define __Pyx_PyUnicode_DATA(u)         ((void*)PyUnicode_AS_UNICODE(u))
   /* (void)(k) => avoid unused variable warning due to macro: */
   #define __Pyx_PyUnicode_READ(k, d, i)   ((void)(k), (Py_UCS4)(((Py_UNICODE*)d)[i]))
+  #define __Pyx_PyUnicode_IS_TRUE(u)      (0 != PyUnicode_GET_SIZE(u))
 #endif
 
 #if CYTHON_COMPILING_IN_PYPY