[main-] fail moveToRow if row idx is past the sheet end

Previously, moveToRow() would return True, and set the cursor
row index to the nonexistent row, with no visible errors.
For slow loading sheets, checkCursor() could then move
the cursor to an earlier row.

visidata/cmdlog.py

@@ -87,7 +87,7 @@ def isLoggableSheet(sheet):
 def moveToRow(vs, rowstr):
     'Move cursor to row given by *rowstr*, which can be either the row number or keystr.'
     rowidx = vs.getRowIndexFromStr(rowstr)
-    if rowidx is None:
+    if rowidx is None or rowidx >= vs.nRows:
         return False
 
     vs.cursorRowIndex = rowidx