When skipping a macro definintion because of an error, apply the same handling

regarding .endmacro as when the macro is parsed regularily: A .endmacro ends
the macro only if is the first token on a line.

src/ca65/macro.c

@@ -373,20 +373,22 @@ static void MacSkipDef (unsigned Style, const FilePos* StartPos)
 /* Skip a macro definition */
 {
     if (Style == MAC_STYLE_CLASSIC) {
-        /* Skip tokens until we reach the final .endmacro. Be liberal about
-        ** .endmacro here since we had errors anyway when this function is
-        ** called.
+        /* Skip tokens until we reach the final .endmacro. Implement the same
+        ** behavior as when parsing the macro regularily: .endmacro needs to
+        ** be at the start of the line to end the macro definition.
         */
+        int LastWasSep = 0;
         while (1) {
             if (CurTok.Tok == TOK_EOF) {
                 ErrorExpect ("Expected '.ENDMACRO'");
                 PNotification (StartPos, "Macro definition started here");
                 break;
             }
-            if (CurTok.Tok == TOK_ENDMACRO) {
+            if (CurTok.Tok == TOK_ENDMACRO && LastWasSep) {
                 NextTok ();
                 break;
             }
+            LastWasSep = (CurTok.Tok == TOK_SEP);
             NextTok ();
         }
     } else {

test/asm/listing/122-errormsg.s

@@ -1,3 +1,3 @@
 .struct         x
-        .word   
+        .word
 .endstruct

test/asm/listing/130-errormsg.s

@@ -1,2 +1,2 @@
         lda     |
-		 
+

test/asm/listing/142-errormsg.s

@@ -0,0 +1,6 @@
+.macro mac
+        .define endmac  .endmacro
+.endmacro
+.macro mac
+        .define endmac  .endmacro
+.endmacro

test/asm/listing/ref/142-errormsg.err2

@@ -0,0 +1,2 @@
+142-errormsg.s:4: Error: A macro named 'mac' is already defined
+142-errormsg.s:1: Note: Previous definition of macro 'mac' was here