cmd: Handle lines with just spaces in bracket blocks.

programs/cmd/tests/test_builtins.cmd

@@ -1029,6 +1029,32 @@ if not exist %windir% (
 ) else (
   echo windir does exist
 )
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@space@
+) else echo block containing a line with just space seems to work
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@tab@
+) else echo block containing a line with just tab seems to work
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@space@@tab@
+) else echo block containing a line with just space and tab seems to work
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@tab@@space@
+) else echo block containing a line with just tab and space seems to work
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@space@
+@space@
+) else echo block containing two lines with just space seems to work
+if 1 == 0 (
+   echo 1 == 0 should not be true
+@tab@
+@tab@
+) else echo block containing two lines with just tab seems to work
 echo --- case sensitivity with and without /i option
 if bar==BAR echo if does not default to case sensitivity
 if not bar==BAR echo if seems to default to case sensitivity

programs/cmd/tests/test_builtins.cmd.exp

@@ -707,6 +707,12 @@ comparison operators surrounded by brackets seem to work
 comparison operators surrounded by brackets seem to work
 windir is defined
 windir does exist
+block containing a line with just space seems to work
+block containing a line with just tab seems to work
+block containing a line with just space and tab seems to work
+block containing a line with just tab and space seems to work
+block containing two lines with just space seems to work
+block containing two lines with just tab seems to work
 --- case sensitivity with and without /i option
 if seems to default to case sensitivity
 if /i seems to work

programs/cmd/wcmdmain.c

@@ -2326,6 +2326,7 @@ WCHAR *WCMD_ReadAndParseLine(const WCHAR *optionalcmd, CMD_LIST **output, HANDLE
             } else break;
           }
 
+          extraData = WCMD_skip_leading_spaces(extraData);
         } while (*extraData == 0x00);
         curPos = extraSpace;