Fix expression (flow) from forming for expression (text)

Related-to: mdx-js/mdx-analyzer#480.

Author: wooorm

grammar.yml

@@ -1434,7 +1434,7 @@ repository:
   extension-mdx-expression-flow:
     if: mdx
     # See <https://github.com/wooorm/markdown-rs/blob/2498e31/src/construct/mdx_expression_flow.rs>.
-    begin: var(before)(\{)
+    begin: var(before)(\{)(?!.*\}[\t ]*.)
     beginCaptures:
       1:
         name: string.other.begin.expression.var(suffix).js

source.mdx.js

@@ -1555,7 +1555,7 @@ const grammar = {
       ]
     },
     'extension-mdx-expression-flow': {
-      begin: '(?:^|\\G)[\\t ]*(\\{)',
+      begin: '(?:^|\\G)[\\t ]*(\\{)(?!.*\\}[\\t ]*.)',
       beginCaptures: {
         1: {
           name: 'string.other.begin.expression.mdx.js'

source.mdx.tmLanguage

@@ -2322,7 +2322,7 @@
       <key>extension-mdx-expression-flow</key>
       <dict>
         <key>begin</key>
-        <string>(?:^|\G)[\t ]*(\{)</string>
+        <string>(?:^|\G)[\t ]*(\{)(?!.*\}[\t ]*.)</string>
         <key>beginCaptures</key>
         <dict>
           <key>1</key>