Fix typo: 'is an error occurred' in documentation

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6229)

doc/man3/CMS_get0_SignerInfos.pod

@@ -55,7 +55,7 @@ CMS_SignerInfo_set1_signer_cert().
 
 Once all signer certificates have been set CMS_verify() can be used.
 
-Although CMS_get0_SignerInfos() can return NULL is an error occur B<or> if
+Although CMS_get0_SignerInfos() can return NULL if an error occurs B<or> if
 there are no signers this is not a problem in practice because the only
 error which can occur is if the B<cms> structure is not of type signedData
 due to application error.

doc/man3/CMS_get1_ReceiptRequest.pod

@@ -54,7 +54,7 @@ CMS_verify().
 CMS_ReceiptRequest_create0() returns a signed receipt request structure or
 NULL if an error occurred.
 
-CMS_add1_ReceiptRequest() returns 1 for success or 0 is an error occurred.
+CMS_add1_ReceiptRequest() returns 1 for success or 0 if an error occurred.
 
 CMS_get1_ReceiptRequest() returns 1 is a signed receipt request is found and
 decoded. It returns 0 if a signed receipt request is not present and -1 if

doc/man3/OBJ_nid2obj.pod

@@ -54,7 +54,7 @@ constants.
 
 OBJ_nid2obj(), OBJ_nid2ln() and OBJ_nid2sn() convert the NID B<n> to
 an ASN1_OBJECT structure, its long name and its short name respectively,
-or B<NULL> is an error occurred.
+or B<NULL> if an error occurred.
 
 OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() return the corresponding NID
 for the object B<o>, the long name <ln> or the short name <sn> respectively

doc/man3/SMIME_read_PKCS7.pod

@@ -57,7 +57,7 @@ streaming single pass option should be available.
 =head1 RETURN VALUES
 
 SMIME_read_PKCS7() returns a valid B<PKCS7> structure or B<NULL>
-is an error occurred. The error can be obtained from ERR_get_error(3).
+if an error occurred. The error can be obtained from ERR_get_error(3).
 
 =head1 SEE ALSO