Fix undefined a:block in indent

s:AdjustBlockIndent() had `let block = a:block` without such an argument,
so GetVueIndent() hit E121 for every line in template, script and style.
It was hidden as errors in 'indentexpr' are silent and the function goes
on, but showed up when calling GetVueIndent() directly.

Also return [0, 0] in s:PrevMultilineEmptyTag() when no tag start is
found, instead of no value.

Add ExpectIndentEachLine() for tests to call GetVueIndent() for each
line and check the result.

test/cases/indent-each-line.vim

@@ -0,0 +1,6 @@
+" GetVueIndent() for each line without errors
+let g:test_flatten = 1
+
+function! Check()
+  call ExpectIndentEachLine()
+endfunction

test/cases/indent-each-line.vue

@@ -0,0 +1,24 @@
+<template>
+  <div
+    class="a"
+  >
+    <input
+      type="text"
+    >
+    <p :class="{ a: b }">x</p>
+  </div>
+</template>
+
+<script>
+export default {
+  data() {
+    return { a: 1 }
+  },
+}
+</script>
+
+<style>
+p {
+  color: red;
+}
+</style>

test/run.vim

@@ -91,6 +91,24 @@ function! ExpectTag(lnum, tag)
   endif
 endfunction
 
+" Call GetVueIndent() for each non-blank line from line 2 as when typing it,
+" which shows errors hidden by 'indentexpr', and check the indent
+function! ExpectIndentEachLine()
+  for lnum in range(2, line('$'))
+    if getline(lnum) =~ '^\s*$'
+      continue
+    endif
+    call cursor(lnum, 1)
+    let v:lnum = lnum
+    try
+      call ExpectEqual(GetVueIndent(), indent(lnum),
+            \ printf('GetVueIndent() at line %d', lnum))
+    catch
+      call Fail(printf('GetVueIndent() at line %d: %s', lnum, v:exception))
+    endtry
+  endfor
+endfunction
+
 if filereadable(s:case.'.vim')
   execute 'source '.fnameescape(s:case.'.vim')
 endif