patch 8.0.1249: no error when WaitFor() gets an invalid wrong expression

Problem:    No error when WaitFor() gets an invalid wrong expression.
Solution:   Do not ignore errors in evaluationg the expression.  Fix places
            where the expression was wrong.
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index eb43cf4..d6033d5 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -125,15 +125,12 @@
     let slept = 0
   endif
   for i in range(timeout / 10)
-    try
-      if eval(a:expr)
-	if has('reltime')
-	  return float2nr(reltimefloat(reltime(start)) * 1000)
-	endif
-	return slept
+    if eval(a:expr)
+      if has('reltime')
+	return float2nr(reltimefloat(reltime(start)) * 1000)
       endif
-    catch
-    endtry
+      return slept
+    endif
     if !has('reltime')
       let slept += 10
     endif