fixes rst parsing Markdown CodeblockFields blocking the loop (#24128)

```nim
import packages/docutils/[rst, rstgen]

let message = """```llvm-profdata"""

echo rstgen.rstToHtml(message, {roSupportMarkdown}, nil)
```

lib/packages/docutils/rst.nim

@@ -1526,7 +1526,7 @@ proc parseMarkdownCodeblockFields(p: var RstParser): PRstNode =
     result = nil
   else:
     result = newRstNode(rnFieldList)
-  while currentTok(p).kind != tkIndent:
+  while currentTok(p).kind notin {tkIndent, tkEof}:
     if currentTok(p).kind == tkWhite:
       inc p.idx
     else:

tests/stdlib/trst.nim

@@ -16,6 +16,8 @@ discard """
 [Suite] RST escaping
 
 [Suite] RST inline markup
+
+[Suite] Misc isssues
 '''
 matrix: "--mm:refc; --mm:orc"
 """
@@ -1980,3 +1982,13 @@ suite "RST inline markup":
           rnLeaf  ')'
       """)
     check(warnings[] == @["input(1, 5) Warning: broken link 'f'"])
+
+suite "Misc isssues":
+  test "Markdown CodeblockFields in one line (lacking enclosing ```)":
+    let message = """
+    ```llvm-profdata merge first.profraw second.profraw third.profraw <more stuff maybe> -output data.profdata```"""
+
+    try:
+      echo rstgen.rstToHtml(message, {roSupportMarkdown}, nil)
+    except EParseError:
+      discard