Fix handling of spaces in shebangs.

ShellCheck/Parser.hs

@@ -2345,8 +2345,10 @@ ifParse p t f =
 prop_readShebang1 = isOk readShebang "#!/bin/sh\n"
 prop_readShebang2 = isWarning readShebang "!# /bin/sh\n"
 prop_readShebang3 = isNotOk readShebang "#shellcheck shell=/bin/sh\n"
+prop_readShebang4 = isWarning readShebang "! /bin/sh"
 readShebang = do
-    try readCorrect <|> try readSwapped
+    try readCorrect <|> try readSwapped <|> try readMissingHash
+    many linewhitespace
     str <- many $ noneOf "\r\n"
     optional carriageReturn
     optional linefeed
@@ -2359,6 +2361,15 @@ readShebang = do
         parseProblemAt pos ErrorC 1084
             "Use #!, not !#, for the shebang."
 
+    readMissingHash = do
+        pos <- getPosition
+        char '!'
+        lookAhead $ do
+            many linewhitespace
+            char '/'
+        parseProblemAt pos ErrorC 1104
+            "Use #!, not just !, for the shebang."
+
 verifyEof = eof <|> choice [
         ifParsable g_Lparen $
             parseProblem ErrorC 1088 "Parsing stopped here. Invalid use of parentheses?",