Fix crash when creating virtual table on API <= 15
Fix crash when creating virtual table on API <= 15

The CREATE VIRTUAL TABLE command doesn't support IF NOT EXISTS prior to
version 3.7.11, which officially appears in API 16 (JellyBean).

KrzysztofWrobel/squidb,KrzysztofWrobel/squidb,KrzysztofWrobel/squidb