plist: fix inverted strcmp in string to boolean conversion

plist_dict_get_bool() compared the string value with strcmp() but treated a
non-zero return as a match. strcmp() returns 0 on equality, so the conditions
were inverted: "true" produced 0, "false" produced 1, and any other string
also produced 1. The error branch could never be reached, since it required
both comparisons to return 0 at once.

The result is that the API returns the opposite of the stored value for both
valid boolean strings, and returns true for strings that are not booleans at
all, instead of reporting the conversion error.

Compare == 0 in both conditions:

  input          before   after
  true           0        1
  false          1        0
  not-a-bool     1        error
  TRUE           1        error
  (empty)        1        error

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

src/plist.c

diff --git a/src/plist.c b/src/plist.c
index 5ea6c12..bcd212c 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -1495,9 +1495,9 @@
 	case PLIST_STRING:
 		strval = plist_get_string_ptr(node, NULL);
 		if (strval) {
-			if (strcmp(strval, "true")) {
+			if (strcmp(strval, "true") == 0) {
 				bval = 1;
-			} else if (strcmp(strval, "false")) {
+			} else if (strcmp(strval, "false") == 0) {
 				bval = 0;
 			} else {
 				PLIST_ERR("%s: invalid string '%s' for string to boolean conversion\n", __func__, strval);