Ensure that aggregate functions are not used when evaluating a default
value for a table column.
Candidate fix for ticket [3a88d85f36704eebe134f7].

FossilOrigin-Name: 29ba812825bf06ef230f2480bba0579653f0a52d
diff --git a/src/expr.c b/src/expr.c
index e6ac84d..9eb893d 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -2768,6 +2768,11 @@
         sqlite3ErrorMsg(pParse, "unknown function: %.*s()", nId, zId);
         break;
       }
+      if( pDef->xFunc==0 ){
+        sqlite3ErrorMsg(pParse, "misuse of aggregate function: %.*s()",
+                        nId, zId);
+        break;
+      }
 
       /* Attempt a direct implementation of the built-in COALESCE() and
       ** IFNULL() functions.  This avoids unnecessary evalation of