implement sqlite3_column_text_not_null in datastore/sqlite.nim

consolidate calls re: `SQLiteDatastore.new` and `idCol`

datastore/sqlite.nim

@@ -143,25 +143,11 @@ template journalModePragmaStmt*(env: SQLite): RawStmtPtr =
     return failure $sqlite3_errstr(x)
 
   let
-    x = sqlite3_column_text(s, 0).cstring
+    x = $sqlite3_column_text_not_null(s, 0)
 
-  # detect out-of-memory error
-  # see the conversion table and final paragraph of:
-  # https://www.sqlite.org/c3ref/column_blob.html
-  # see also https://www.sqlite.org/rescode.html
-
-  # in order to detect an out-of-memory error check that the result is a null
-  # pointer and that the result code is an error code
-  if x.isNil:
-    let
-      code = sqlite3_errcode(sqlite3_db_handle(s))
-
-    if not (code in [SQLITE_OK, SQLITE_ROW, SQLITE_DONE]):
-      raise (ref Defect)(msg: $sqlite3_errstr(code))
-
-  if not ($x in ["memory", "wal"]):
+  if not (x in ["memory", "wal"]):
     s.dispose
-    return failure "Invalid pragma result: \"" & $x & "\""
+    return failure "Invalid pragma result: \"" & x & "\""
 
   s
 
@@ -245,3 +231,21 @@ proc query*(
 proc release*[T](x: var AutoDisposed[T]): T =
   result = x.val
   x.val = nil
+
+proc sqlite3_column_text_not_null*(
+  s: RawStmtPtr,
+  index: cint): cstring =
+
+  let
+    text = sqlite3_column_text(s, index).cstring
+
+  if text.isNil:
+    # see the conversion table and final paragraph of:
+    # https://www.sqlite.org/c3ref/column_blob.html
+    # a null pointer here implies an out-of-memory error
+    let
+      code = sqlite3_errcode(sqlite3_db_handle(s))
+
+    raise (ref Defect)(msg: $sqlite3_errstr(code))
+
+  text

datastore/sqlite_datastore.nim

@@ -117,22 +117,7 @@ proc idCol*(
   checkColMetadata(s, index, idColName)
 
   return proc (): string =
-    let
-      text = sqlite3_column_text(s, index.cint)
-
-    # detect out-of-memory error
-    # see the conversion table and final paragraph of:
-    # https://www.sqlite.org/c3ref/column_blob.html
-
-    # the "id" column is NOT NULL PRIMARY KEY so an out-of-memory error can be
-    # inferred from a null pointer result
-    if text.isNil:
-      let
-        code = sqlite3_errcode(sqlite3_db_handle(s))
-
-      raise (ref Defect)(msg: $sqlite3_errstr(code))
-
-    $text.cstring
+    $sqlite3_column_text_not_null(s, index.cint)
 
 proc dataCol*(
   s: RawStmtPtr,